DEAR MISS MANNERS: With the advent of so many ways to communicate, I am sometimes at a loss to know how to avoid misunderstandings and missed messages attributable to using the wrong medium.

Some of my friends and acquaintances prefer telephones to email, while others prefer text messages. Some prefer landlines to mobile phones, etc., ad infinitum.

Is there a rule, or at least an expectation, that one should reply to a message in the same medium in which it was proffered?

GENTLE READER: It is getting so that one has to keep dossiers on one’s friends: what do they refuse to eat, what forms of address (honorifics, surnames) do they find insulting, and now, what forms of communication do they refuse to use.

So yes, it would help to notice the means in which messages are sent, and to respond in kind. Miss Manners realizes that acceding to that preference deprives the flexible person of choice. But, then, those who will not speak by telephone and those who do not communicate by keyboard are not going to have a future together, anyway.

DEAR MISS MANNERS: Is it appropriate to bring my girlfriend to a first-time family reunion?

GENTLE READER: Only if you will find it appropriate for every single member of your family to ask her when you are getting married.

DEAR MISS MANNERS: I am lucky enough to be living in a coastal area with abundant seafood. Mussels are inexpensive and fun to cook with, plus they show up on the menu of several local restaurants.

But how does one eat mussels in the shell -- in, say, a soup or sauce-laden dish -- without making a mess of it?

GENTLE READER: Mussels are considerate little creatures, in that they provide you with a tool with which to enjoy them.

That is, Miss Manners has never seen one actually hand over a seafood fork, which is what you would use to pry them from their shells. But after that, they provide the spoon-shaped shell with which you can properly enjoy the sauce.

DEAR MISS MANNERS: My granddaughter invited two cousins and their families to her wedding. Both of their responses were to return the RSVP with the “Regret” portion ticked. There was no other communication such as a note or phone call to explain why they could not attend. My granddaughter is an only child, and these cousins are two of her closest relatives.

Am I correct in assuming that they owed her some reason for not being at her wedding? As recipients of the invitation, should they send a wedding present?

GENTLE READER: No, they do not owe a reason, and they do not owe a present. What they owe, in all decency, is an expression of regret at not being able to attend, along with their good wishes.

But Miss Manners notices that the invitation itself invited that curt response by providing a place to decline with a mere check. Apparently it already expressed regret, which is an odd thing for the host to presuppose.

(Please send your questions to Miss Manners at her website, www.missmanners.com; to her email, dearmissmanners@gmail.com; or through postal mail to Miss Manners, Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO 64106.)

DEAR MISS MANNERS: Is it rude to announce that today is your birthday, either in person or on social media? I’ve always thought people jubilantly declaring “It’s my birthday!” were just begging for birthday wishes or gifts. It seems tasteless. What are your thoughts?

GENTLE READER: That yes, after a certain age -- say, 12 -- one does not enter a room, or the social media equivalent, by announcing one’s own birthday.

If, however, it can be coyly and casually folded into the conversation -- for example, as the answer to “How are you?” -- Miss Manners would not fault your enthusiasm.

DEAR MISS MANNERS: We have three cats. When we have guests for the first time, I try to remember to mention we have cats since some people are allergic, while others just don’t like them. However, sometimes I don’t think about it when extending an invitation.

Whose responsibility is it to raise the issue: the host’s or the guest’s? If someone has a food allergy and is coming for dinner, I assume they will let me know. Is it the same for pets?

GENTLE READER: No. And, Miss Manners notes, it is not the case for food allergies, either, unless it is something life-threateningly severe. Guests should not be vetting their hosts for all allergen possibilities and making guesses at both what is being served and who will be present. And they should definitely not be voicing and listing all of their mere dislikes and preferences, even if asked.

It is, however, generally polite that a host inquire about allergies before preparing a meal, and inform guests of any allergy-producing pets. If, as in your case, you forget, let them know when you remember -- or as they come through the door -- and do everything reasonable to isolate or eliminate the offenders. It should be noted, however, that this rule does not apply to any equally offensive humans.

DEAR MISS MANNERS: We often meet friends at restaurants. If one party arrives ahead of the other, should they go to the table or wait for the other party to arrive so they can all be seated at the same time?

I would like to wait for them, but one couple always seems to arrive before us and they go to the table without us, even if I have made the reservation. Should I care, or not?

GENTLE READER: Not. Restaurant rules differ from dinner parties at one’s home. At the latter, guests wait to be seated until their hosts indicate that it is time to do so, and are seated themselves.

Miss Manners is surprised, however, that the situation you described has been an issue at restaurants, as most do not even allow only part of the party to be seated for fear of losing a bigger table if the others do not show. If your friends are able to get hold of a table, why not let them? If it helps, you may consider that the host in this case is the restaurant itself. And securing a table is infinitely preferable to being jostled in a crowded hallway.

(Please send your questions to Miss Manners at her website, www.missmanners.com; to her email, dearmissmanners@gmail.com; or through postal mail to Miss Manners, Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO 64106.)

DEAR MISS MANNERS: What is the proper etiquette to join a conversation already in progress?

For example, at a social gathering, a couple of people are already having a conversation. Is it OK to approach the group and say “hello,” or do I approach the group and wait for them to acknowledge me?

When someone approaches my group conversation, I always acknowledge the person right away and share the topic we are discussing. Most of the time, I approach a group and say “hello,” but is this considered interrupting? A few times, I have walked up to a conversation and stood there and was never acknowledged. Very awkward. Help ... I don’t want to be rude, but I love to talk too!

GENTLE READER: Inserting oneself into a conversation in progress, like cutting in for a dance, does have its own etiquette. The newcomer must wait for a lull in the conversation, acting in the interim as if what is being said is both interesting and, even without the preamble, intelligible.

The established group is required to assume the opposite, namely that the newcomer does not know what is being said, and is therefore entitled to a brief, explanatory aside. At the next natural break, introductions can be made all around. While a group holding a conversation in a social gathering should welcome newcomers, Miss Manners warns that such will not always be the case. It is therefore best to actually listen to what is being said, in case it is time to beat a hasty retreat.

DEAR MISS MANNERS: Is dancing to or parodying the national anthem disrespectful?

GENTLE READER: Yes. But isn’t that why you thought of it?

Miss Manners cannot often count on the public to enforce proper behavior, except when it concerns slights to themselves. And perhaps that is just as well. But this would certainly bring it on, and it is not likely to be gentle.

She would advise you to go no further with this idea, which is as unwise as it is unfunny.

DEAR MISS MANNERS: My mother invited her family on a cruise, where we dined nightly in the main cabin. My 54-year-old sister’s manners were a nightmare. My mother was visibly embarrassed in front of her new husband.

I suggested to my sister to follow the level of formality and cues from our mother. She said I was being judgmental. How do you help someone understand that manners matter?

GENTLE READER: Without justifying your sister’s behavior, Miss Manners notes that 54 years is a long time to wait before attempting to correct a problem. At least your sister cannot accuse you of rushing to judgment.

Your mother will need to talk to her, admitting that she bears some responsibility for not speaking sooner. She must resist the temptation to justify her tardiness by blaming it on the newcomer (“your new stepfather was appalled”), as he was minding his own business.

(Please send your questions to Miss Manners at her website, www.missmanners.com; to her email, dearmissmanners@gmail.com; or through postal mail to Miss Manners, Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO 64106.)