Flocking is the process of applying a thin layer of artificial snow to a Christmas tree. While flocking can add a nice touch of realism to your tree, it is important to be aware of its potential toxicity to cats. Some flocking materials can contain formaldehyde, which is a known carcinogen that can cause respiratory irritation, nausea, and other health issues in humans and animals. Additionally, some flocking materials may contain other chemicals that can be harmful if ingested. To keep your cat safe, it's best to avoid using flocking on your Christmas tree and opt for other decorations instead.