Maybe he heard her rolling a bunch of paper out? Or maybe he had a lot left but she used the remaining of the roll? Honestly, I had a few instances when I had to use A LOT of toilet paper. I have no clue if that's what happened in that case. Either way, somehow he knew. Or maybe he just assumed. Maybe it's a fictional story after all.

And yet, there are people out there who would scold you for similar things. It may not be toilet paper but something else.