The Rainbow Bridge is the theme of several works of poetry written in the 1980s and 1990s that speak of an other-worldly place where pets go when they die, eventually to be reunited with their owners. One is a prose poem whose author is unknown. The other is a six-stanza poem of rhyming pentameter couplets, created by a couple to soothe the pain of losing a pet. Each piece has gained popularity around the world among animal lovers who have lost a pet

The belief has many antecedents, including similarities to the Bifrost bridge of Norse mythology.

 Many Christians interpret the Bible to say that all living things (animals) have soul and will go to a paradise when they die. This may be a stretch, but certainly the Bible is open to the idea.(Ecclesiastes 3:21

Psychics and channels often report of contacting deceased pets or being contacted by them.

A recent ABC News poll showed that 47% of pet owners believed their pets would go to heaven. 

When the question is raised as to whether or not pets have "souls", we suggest you check the definitions of soul and spirit  in our dictionary.