Though cats and snails are natural enemies, the cats are surprisingly relaxed--not a trace of fear from either one. Shiro is so peaceful that he's almost asleep, rousing only to kiss his companion. Kuro noses the snail curiously, who responds in kind. It's the beginning of a beautiful friendship.
How did the snail end up on Shiro? His owner has a great hobby: putting objects on Shiro to see how he will react.
-via Rocket News 24
See also: More of the Shironeko cats.