Oh right, I seem to have forgotten that step in beating the boss. Is it that shooting the stomach-head triggers baddies to spawn?

And do you have to scream at the stomach-head to damage him, or can you just scream near the stomach and he will be damaged regardless? If it's the later, then you can ignore my previous advice about screaming, and sorry for any possible confusion that I may have caused.

Oh, and I finished the game, it's just that my last playthrough was a while ago, so I may not be remembering certain things correctly.