Pronounced gon-dee-eye — A protozoan parasite, which reproduces in the stomachs of cats, and develops in mice who eat the cat's feces.
It is interesting here because of the effect it has on the behavior of mice. Specifically, it causes the mouse to find the smell of a cat to be irresistible.
What does this do? It gets the parasite back into the stomach of a cat, where it can, once again, reproduce.
The circle of life. :-)
It is also interesting here because it has been implicated as one (of many) possible causes for schizophrenia in humans whose mothers have been exposed to it during pregnancy.