Ed Yong, writing at Not Exactly Rocket Science:
T.gondii (or Toxo for short) infects a wide variety of mammals, but it only completes its life cycle in the guts of a cat. To get there, Toxo has ways of subverting the behaviour of dead-end hosts like mice. Its machinations are subtle, so subtle that it’s normally hard to tell an infected mouse from an uninfected one. But the difference becomes obvious when there’s cat pee in the air. Normal mice, even lab-born ones that have never met a cat, have an innate fear of cat smells. Those infected with Toxo do not. They (and their parasites) are more likely to end up in a cat.