As it happens, there might not be a puppet like that you can buy, but years ago McDonalds gave away these plastic Grimace puppets.
http://image.timepassagesnostalgia.com/watermarked/imagesa9/a917grimacex16.jpg
At one of the Michigan comic cons, a guy named Sean Bieri, who is a great cartoonist, got a hold of a stack and would draw a little alien head on his finger. then he’d put on the puppet, have Grimace begin to talk, then convulse, and then the alien would burst out from his stomach. I think I watched him do that bit like 5 times and it just got funnier. Somewhere I have a photo to prove it.
Sean rocks.