The snake repellent thread prompted me to look up “mongoose” on wikipedia. Apparently their taxonomic family is “herpestidae”.
Now, I know just enough Latin to be dangerous, but I recognize that “herpe-” signifies something to do with snakes (whence, “herpetology”). But I’m curious – does the family name derive from their reputation as snake-fighters, or because (as mammals go) they’re kind of shaped like snakes?
Herpestidae (the family name) is derived from the name of the genus Herpestes, and that seems to be derived from Greek words meaning “creeping thief”.
Aha! I have inspired learning with my blatherings! 
Ah, none of the above, then.
In the interest of completeness, I looked up “herpetology” in the OED. It, too, comes from the same Greek “herpein”, meaning to creep. And, if you’re wondering, this is also the root of “herpes”.
So while the naming of the mongoose family doesn’t actually have anything to do with snakes directly, it turns out that they have a similar name because both are “creepy”.
Nobody seems to know where the term Herpestes comes from – it appears to be the Latin for “mongoose.” Mongoose is an anglicization of two Drvidian terms (meaning “mongoose” of course) Telego mungeesa and Kannada mungus, probably through Marathi mangus, an obvious borrowing from the Dravidian terms. The English spelling seems to have adapted to -goose. Two or more of the little critters, though, are mongooses, not ‘mongeese’.
I have a hunch – nothing provable – that herpestes derives from “snake predator” or something of the sort.