Play the Stubbs vs. Chief Masters Dance Battle and get a "Perfect" rating in all rounds (including the bonus one) to see a bonus sequence with a hovering limousine.
Developer commentary
Collect the hidden hippo heads in Insane mode to hear a developer commentary track.
Funny comments
Sometimes people will say funny things, such as:
"You're gonna die! Again.."
"I see a Zombie."
"Have some punch!"
"I'll show you hard science!"
"Let me give you a hand!"
"I loved that arm!" (cry)
"Aw, my mother gave me that arm!"
"Forget science! Kill! Kill! Kill!"
"My beautiful mind!"
"Not the face!"
"Why did I choose science? I could've been a talk show host!"
Funny hand gesture
When you throw your hand, occasionally it will put its middle finger up to you. This also happens when you jump as the hand.