The nice thing that happened in class today:

Grade 5 students solve a puzzle where they put cuneiform numbers in order (there is no guidance, just work with the symbols, how do you order them?)

I told them they are like archeologists cracking a code. They did it!

"But where is zero?"
"It wasn't invented yet." I said this seriously. I mean ... it's true.

Later that day the same student asked if it was a joke. I got to tell them no! Zero had to be invented. Everything had to be invented!