surviving 4th graders questions

setting: 1:00pm, my classroom with all the students (13 of them) for music class
things to remember: our school has no air conditioning

the conversation happens as such
i am up at the board telling the something profound about the music they are learning for the christmas program.
one of the 4th graders: "miss s, what is that wet stuff under your arms?"
me: "that would be sweat"
the student: "oh"
the rest of the students: "giggle, giggle, tehehehe"

me: slightly embarrassed