Slugs are not naturally poisonous to dogs; however, they pose a significant health risk because they can carry a deadly parasite called lungworm (Angiostrongylus vasorum). Dogs can become infected by eating slugs or snails or by licking slug slime that contains lungworm larvae. Lungworm infection can be fatal, affecting the heart and lungs, causing symptoms such as breathing difficulties, seizures, and bleeding disorders. Furthermore, slugs can sometimes be contaminated with toxic slug and snail bait, which is poisonous to dogs. Therefore, while slugs themselves are not poisonous, they can indirectly cause serious harm to dogs through parasite transmission or poisoning by bait. If a dog eats a slug, it is advisable to contact a veterinarian for advice and possibly get early treatment to avoid severe complications.