The humor in this meme derives from the fact that there is a sheep lying on its back with legs in the air, resembling a dog playfully laying down, which is a visual pun on the term 'sheepdog'. The sheep's pose implies a playful, dog-like nature being sold as a 'sheepdog', which is funny due to the absurdity and role reversal, as sheepdogs are traditionally the ones herding sheep.