Bowels was probably not as accurate as innards, and to be honest the implications that the word bowels brings across is probably not something that Bruce would like in a song--if this ever becomes a song. He's still hoping for 'no', personally, although he's sure that his personal opinion doesn't really apply.

"Maybe you should rework that entire line," he responds instead. "Especially if children are going to hear that." It wasn't exactly the most friendly of images to project to them, after all.