Cats are curious creatures, and Christmas trees are like big, moving, living toys to them. The lights, the ornaments, and the branches are all things that are new and exciting for them to explore. Plus, they can climb up and hide among the branches, making for a fun game of hide-and-seek. Some cats may even try to eat the needles or chew on the lights, so it's important to keep a close eye on them around the tree.