I believe when humans die they either go to heaven or hell. I want to know what happens ahen an animal dies.?

According to The Bible, they go to 'hell'. Here's how that's the case, and what it really is.

The term 'hell' as used in the scriptures comes from the Greek and Hebrew terms 'Sheol' and 'Hades', both which refer to the common grave. When they go there, they return "to the dust". Basically they break down to the bare elements they were created from and cease to exist. (Ecclesiastes 3:19-20) During this process they feel/know nothing; completely unconscious. (Ecclesiastes 9:5, 6 & 10)

(New World Translation of the Holy Scriptures)