So does using the cold tap from any sink in the house. As long as cold water is being diverted to somewhere else while the shower is on, it'll make it hotter. The opposite is also true, use hot water and they'll have a cold shower
I think the music notes in the first panel would be better suited not having the splatter effect; it fits the second panel- a screeching halt to his singing. And maaaybe a slightly more pained expression? I dunno that might not need it.
Anyway it's really amazing!! Love the suds covering him