No, it’s not a vigorous ballet. 
So what is that stinky stuff that accumulates under most everyone’s toenails? At least most everyone I’ve known.
I shower every day, sometimes twice, and I pay particulat attention to my feet. But I can always dig out a little of it. Can’t resist a sniff, I’ll admit.
It doesn’t grow under our fingernails.
So, seriously now, do any of the great minds of the SDMB know?
Extra point for those who suck their partners toes;
Doesn’t toe jam gross you out? I mean, you’re eating it!
I can’t believe I beat aha to this one. 
Peace,
mangeorge
My WAG - mostly sweat ‘n’ sock lint. Thank you for helping me forget my hunger.
some of it is dead skin cells from under your nail. Fingernails have this too, but are not cooped up in socks and shoes so they don’t get so funky.
The stuff that collects under the toenails: I have always heard it referred to as toe cheese, not toe jam. See The cheese that you don’t buy in stores
The stuff that collects between the toes: Cecil claims this is called toe jam. See What is “toejam,” as in “toejam football”?