I think he didn’t pronounce his ‘y’ as ‘uh’, that’s a dead giveaway. repeat after me: zunnonums (I actually listened to German giving an English presentation and he always pronounced symbol as zumbl).
Physically, it’s impossible for Calvin to flood the bathroom without mum noticing and then mum standing knee-deep in still water, as she first has to open de door to get in, but who cares… I think this “error” makes it even more funny.
The truth hurts: the truth is that he got beaten and it really seems to hurt.