Here are a couple of factoids about the Pacific banana slug.
They are the second largest terrestrial slug (the largest being the European Limax cinereoniger -- uppity Europeans, thinking you're so clever with your huge slugs...).

Like most slugs, they come equipped with two pairs of sensory tentacles. The
upper, larger pair (called eyestalks) can perceive light, while the
lower two detect chemicals. Both can be retracted.
The breathe through a single lung. The slime they secrete to aid in avoiding dehydration is also laden with pheromones to aid in mating. The slimy scent is the slug equivalent of a human's 'come hither' curled finger.

These creatures, like most (all?) slugs, are hermaphrodites, and mating consists of exchanging sperm with each other. It's a slug mating quid-pro-quo.

Source