An Australian man contracted Rat Lungworms (you can NOT make this up), from eating two garden snails on a dare. The snails picked up the Lungworms from rodent droppings.
The Lungworms are a parasite called Angiostrongylus cantonensis, and if ingested can cause fatal swelling of the brain. The disease is more common in Thailand, where raw snail meat is eaten.
Please, do not eat garden slugs; especially raw.