Not every banana-coloured slug in the forest is a Banana Slug. The colour of European slugs varies hugely and can be close to that of the native forest-dwellers.
One of the ways to sort out the Banana Slugs from the Euro-invaders, is that the home team are smooth, whereas the European ones have a smooth mantle, but a ridged back or keel. They often have a an orange stripe around the edge of their single, muscular foot.
Slugs and snails most certainly differ from puppy dogs' tails, but not very much from each other. A slug is a snail whose shell has evolved to become a leathery mantle. But this means they have lost the protection of the shell. No matter, they have their slime. It helps to stop dehydration, protects their soft body parts from rough surfaces and allows them to make themselves into an unpleasant tasting ball. It also plays a part in the mating ritual.
Slugs don't have those girl-boy issues, they are hermaphrodites, so they all have both sets of sex organs. A lot of people know this, but then sometimes think this means they don't need to encounter another slug to reproduce. Oh they do. In fact both slugs taste each other's slime.If both approve, they both display their male organs, which they insert into the other's female organs. And they really need to be sure about each other. If one slug is significantly bigger than the other, then their male organ may not fit, it may come unstuck and have to be gnawed off by the other. Slug sex is not for the faint-hearted!
They both go away and in the fullness of slug-time, will lay their batches of translucent eggs in some damp, sheltered place, often beneath logs or in holes in the ground. Slugs have no parenting skills, they make their getaway on their one slimy foot, leaving the eggs to hatch and the sluglings to the mercy of frogs, snakes, birds, skunks and whatever doesn't mind the taste.
Picture of banana slug from http://www.birdsamore.com/critters/slugs.htm