There is a protozoa parasite called toxoplasma which can only reproduce in the guts of cats. This parasite is then excreted in cat feces which is then eaten by rodents. Rodents normally have an instinctual aversion to cats. The toxoplasma actually changes wiring in the brain of the rodent to make urine seem unbearably attractive. This allows the rodent to be easily eaten by the cat so that the parasite finds its way back into the cat to reproduce. It has been shown that this rewiring is not an accident but is done very specifically by this one parasite to allow it to reproduce.

(The Great Courses – Being Human: Life Lessons from the Frontiers of Science)