crummy mouser, should help keep mice away. Over the millennia, mice and rats
have evolved a strong aversion to the smell of cats and other predators;
laboratory-bred rodents hundreds of generations removed from the wild will freak
out upon catching a mere whiff of cat. Unless, of course, they're somehow
reconfigured not to. In a study published late last year, for instance, Japanese
researchers reported on a strain of mutant mice they'd whipped up that lacked
certain crucial mechanisms for interpreting odors. These mice could smell cats
just fine, but didn't know they were supposed to be afraid: confronted with a
cat, they chose to investigate or even try to play rather than flee.
Another exception that proves the rule is the case of the parasite
Toxoplasma gondii, discussed here a couple years back when the topic
was a possible link between cat poop and schizophrenia. A quick recap: T.
gondii infects a variety of mammals, including rats, but can reproduce only
when the host animal is a cat; one of its evolutionary tricks is to make
infected rats act weird, improving their odds of being caught by cats and
thereby allowing the parasite to spread. A key form of said weird behavior:
T. gondii-infected rats not only fear cat odor less, they're actually
drawn to it. So, since about a third of wild rats carry the parasite, having a
cat in the house will repel the majority of rats but might encourage some in the
minority to stop by.
[Comment: may explain human cat lovers and feeders]
From Straight Dope