Snail

''I caught a snail! Escargot? Escarg-NO!- Animal Crossing: Wild World'' ''I caught a snail! Seriously, though... Could you fail to catch a snail?- Animal Crossing: City Folk

The snail is a small mollusc that can be found moving slowly across flowers during rainy weather. When caught, it hides within its protective shell.

If a Player were to disturb it, the snail would retreat into its shell, fall to the floor and disappear.

Upon Donation in City Folk
Blathers will talk to the Player about the snail if it is donated to the museum:

"Ah, if you didn't know, here's a fact for you... Removing a snail's shell doesn't make it a slug! If you did try to pull off a snail's shell-- which I surely DO NOT condone-- its insides would spill out... I... Just got a mental picture of that. I fear I shall never eat again!"

Further Information
Helix pomatia, also known as the edible snail or escargot, is a species of snail that is sometimes farmed for eating. It is found throughout Europe, but was introduced to Britain by the Romans.