@sozobe,
Oh! That makes perfect sense. At our festivals and fairs, this game usually features miniature fishbowls with snap-on plastic lids. (We've brought several home over the years.) That's the kind of set-up I was imagining.
I'm glad to hear it wasn't a big deal for the girls. Their friendship sounds pretty solid. Unfortunately, when I was their age I was easily intimidated by other girls. I would have given in, then regretted it, then made it into some big hairy deal in my own mind. Pathological, really, but those were the times. Nice girls didn't stick up for themselves. Things have certainly changed for the better!