Question

Why do animals have certain useless organs in their body?

Answer 1

According to me no organ in a human's or animal's body is useless.
You might have heard about appendix as a useless organ but.....
appendix protects good germs for your gut and reboots your digestive system.

Answer 2

Animals do not have useless organs. The each and every organ has its own importance and uses and it is used to perform certain tasks.