Question: why do dogs go crazy when they see cats?

Darren Logan answered on 13 Mar 2012:

Thats a great question, but I’m afraid we don’t know a detailed answer to it yet.

The basic answers is that the dogs are responding instinctively when they smell a cat. If its a smell, then whetever the chemical they are detecting is is binding to some special cells in their nose and this sends a signal to their brain which tells them to chase the cat. We don’t know what that the chemical is because, allthough dogs are among the best smellers in the animal kingdom, there has been very little study on their sense of smell. We have done some experiments to ask why mice are afraid of cats, and we found a chemical that cats produce detected by special cells in the mouse nose.

As for why this happens, we don’t know that for sure either but its probably a side effect of the evolution of dogs from wolves. Wolves would want to have a system that helps them instinctively find food through smell. This system still exists in dogs but its tuned into the signals from cats.