why do dogs want to kill a cat when they see it?

Answer 1

Not all dogs try to, it is all caught up in the prey drive. Animals that have a high prey drive such as poodles, whippets, greyhounds, australian shepards, etc were bred to chase and kill small animals, and the fact that the animal is a domesticated cat doesn't register in them :P. Some dogs that have been raised around cats not only get along with cats, but can be submissive towards them.

Answer 2

different personality perhaps? animals have the sixth sense. maybe the cat maybe an evil cat. not joking. my dog and cat were good to each other though.