As for the zombies, Jockeys' giggling is a form of communication, similar to that of spotted hyenas.
Spitters are a mutated strand of boomette, and chargers are a mutated strand of Tanks.
I actually see Hunters more like cats (lions, tigers, o mai) than dogs. Dogs don't generally CLAW at their victims, don't jump much, generally don't stalk their prey from above, etc. I see them sharing a lot of traits with leopards, actually.
All special infected (aside from Witch and Tank) have male and female varients - Valve was just too lazy to make differing designs for them.
Infected think survivors are mutated monsters, and really only attack out of self preservation. They don't know that THEY'RE the sick ones.
Infected don't eat the bodies of survivors they kill.
Primates are the only ones that can carry the virus. If something other than a human gets infected, the species determines what special infected they become. (Ex. All gorillas would be Tanks, chimps would be Jockeys, baboons would be hunters, orangutans would be smokers, etc)