What do they kill animals for?

It's important to be specific about what you mean by "they" and "kill animals." It's not possible to give a single answer that covers all instances of animal killing. To get a helpful answer, I need more context.

Could you please clarify your question?

For example, do you mean:

* Why do humans kill animals?

* Why do certain cultures kill animals?

* Why do predators kill animals?

* Why do animals kill other animals?

Once I understand your specific question, I can give you a more accurate and relevant answer.