A fluke is a parasitic flat worm, known scientifically as Trematoda. Most flukes are parasites mollusks and vertebrates. A snail is a mollusc. Some people use snail slime as cosmetic creams to reduce wrinkles and clear scars..
Anyway the life cycle of some parasites is just unbelievable. So many things have to happen at such specific moments in order for the parasite to survive. Like the bird fluke. The parasite finds a bird host, grows and produces eggs which will eventually end up in the birds poop. These eggs have to be swallowed by a snail. Let me repeat that, in order for the parasite to live they have to be swallowed by a snail. I guess this happens...often? Then it grows, and I'm guessing the snail has to be eaten by another bird in order for the cycle to continue.