It may look sparkly and pretty, but hanging up string lights outdoors could be hellish for wild animals. When you string lights around trees and bushes, wild animals like birds and deer can get tangled up in the lights. Deer, for example, often scrape their antlers on the sides of trees. During the day -- when the lights aren't so obvious -- they can get caught up and tangled. If you must hang lights, do it near your home, and be sure the lights are attached firmly and out of harm's way.