What, then, could attract rats to cat pee? None other than toxoplasma gondii, a parasite carried by cats. If a rat is infected by t. gondii, cat urine doesn’t seem so bad anymore; it’s even kind of attractive. Even more impressively, Stanford University researchers have found that the rats otherwise behave normally, with all their usual fears intact. The response is so specific that cats and t. gondii seem almost like a single organism — which, in a sense, they are.