Complex sentence: Jerry appears on the TV screen and George hides, then changes the channel, but whatever channel he sets the TV to, Jerry pokes his head out; then Jerry runs back and forth, and he appears big with a scary face.
Split into simpler sentences: Jerry appears on the TV screen and George hides, then changes the channel. But whatever channel he sets the TV to, Jerry pokes his head out; then Jerry runs back and forth, and he appears big and with a scary face.