Angry Birds Space causes my iPhone 4S to run hot?

Other people see the same same? When I run Angry Birds Space, my 4S heats up like it's charging or playing a 3D game.

I can play Kingdom Rush or do other things all day without the phone heating up, but Angry Birds Space can do it after about 10 minutes of play. Only 3D games and charging really heats up my 4S.

Poorly optimized app? Simulating physics, even 2DOF, really does require that much CPU power?

In Kingdom Rush, there'd be many many things going on on the screen at the same time, and I've been pleasantly surprised at how energy efficient it is and my 4S stays it's normal cool self.