I think there are two parts to an animated version of this prop:
- Skeleton pop-up. There's lots of info out there on this. If you did it fast, it probably needs to be pneumatic, but there might also be a way to use an electric motor. On the other hand, if you used a motor and the skeleton slowly sits up out of the body, that might be good too. Maybe better.
- The body. If you notice in the picture, only the lower part of the body is split open. For this to really work, the body would need to be split open from the top of the head all the way down to where the skeleton sits up, sort of like a coat. You might want to look for the various cheap zombie heads and try cutting one open down the front and then reinforcing it with coat hanger wire so it stays open, and leaves space for the skull to move.
You might be able to make it work with only the head being open and then the body could have old clothes on it (a checkered shirt and jeans?) and you wouldn't see the skin there. That way you could make a form that was split open and would leave space for the rib cage. Decorate around it with guts, maybe.
To sum up: The basic gag is that people see a body that's split open, all the way to the skeleton. Then the skeleton sits up! Use a prop controller so it cackles as it does. And figure out what else is in the scene to account for this. Did the person tinker with dark forces that backfired on him? Etc.