And while we're at it, we mean different things by "falling in," too. It doesn't have to bottom out to count as "falling in." All that needs to happen is for there to be significant banging, whether on the bottom, against the far side, or in some other way that hasn't occurred to me yet.

The fact that "banging" isn't a neatly quantifiable term in this context (in others, it's universally understood) does not hinder clear communication among anyone but the aforementioned engineers.