What is the deal with Eric Cartman's hand?

LOL saw both of these episodes. think its just cartmans brain. like when they originally revealed his father like he didnt trust the answer and always didnt trust it. you do know that the first one where they reveal his father was part of april fool joke right. the next week after that they did terrance and phillip episode when everyone wanted to know his father lol. after that they got so many angry responses and said they wouldnt do that again, lol