Homer accidentally kills Lisa's Pony after it eats half his chocolate bar while he is strangling Santa's Little Helper. Now Homer must disguise himself as Lisa's Pony so she won't find out, but his plans go sour we she finds the dead Pony "buried" in her closest. At the end Lisa forgives him when Homer has The Jonas Brothers sing her a song about Ponies.
Hopefully you can do way better than me. Way better.