It stems from the belief that only humans have a soul. Here's an example:

https://www.christianforums.com/threads/animals-dont-have-fe...

I think that view has changed a lot over the last few decades but certainly 30 years ago it was pretty common.

This is not a Christian belief, Augustine and Aquinas (among others) openly believed animals, plants, even stones, had souls. A lot of mistakes regarding Christian theology is people mistaking something they heard '30 years ago' with a millennia old religion

I didn't mean it was an official position of the Church, just one that a lot of Christians have (or at least had fairly recently). Let's not no-true-Scotsman this.

You brought up Christians, not me. Was it meant as a serious claim, or just casual bigotry?

Err yes I did bring it up and it was a serious claim. I'm not sure what your problem with it is tbh.

The thread you posted is one guy who says animals don't have feelings and asking for a Bible verse to support it and a bunch of responders pointing out that animals obviously have feelings.