Kill the Brainpans in the area in order to cross over the "green block things", killing them causes a bridge to be made and you're able to get to the next area. There's one floor where you have to avoid killing a different colored one though. I think it's the green ones you can't kill.

Oh and there's a certain amount you have to kill on each floor in order to move on but I can't remember, usually if you kill all the ones you see you can cross but if not they respawn.