Dog poop!

Today Seth was playing on the couch (he had piled all the pillows onto the floor, a "pillow tower") and he looks down from the couch into the pillows and exclaims "Dog poop!" So I naturally ask him "Dog poop?" "Yes! There is dog poop down there!" I look and don't see anything (obviously there wouldn't be anything seeing as we don't have a dog). Then Seth runs to his bedroom and returns holding a small alien toy and says "See! Dog poop!" "That alien is named dog poop?" "Yes!" Then I extend my hand so I can see the alien and Seth responds with "No Daddy, don't touch the dog poop!" Oh these children of mine.