An attractive girl who is interested in having sex at any given time. A hot version of a skank
Reason: Girls get wet and leave snail trails... ie: they are "snails."
"jonny you need to get to this party asap, it's crawling with snails"
"man you should've seen this snail. she gave me a throbbing blue steel the cat wouldn't scratch. i was about to fold her in half squishy side out right there at the library."