All I know for sure is that it causes animals to froth at the mouth and become violent. It also causes hydrophobia (fear of water). These things are also tragically manifest in people, but it just makes them more sick and crazy then that. It's treatable, but the shot are really painful.
No one wants to see a cat destroyed, and no one wants poor Kyle to get rabies, but it's sure fun as hell to tease him about it.
C