Mary Lynn Rajskub first played Gail the Snail in season five (Picture: FX/Rex)

It’s Always Sunny in Philadelphia star Mary Lynn Rajskub has explained why her character Gail the Snail is so gross… outlining exactly who is to blame.

In season five of the hit sitcom, Mary, 49, is introduced as Gail the Snail, the unpleasant cousin of Dennis Reynolds (Glenn Howerton) and his twin sister Dee Reynolds (Kaitlin Olson).