The default Python code contains an error. In the section “Don’t change the following code:”, the line if t < 30: references an undefined variable t when it should be time.
The arrows barrage animation is a bit off, sometimes it does not have a “hole” for the hero to pass through (although the hero does not take damage from it as long as the code is correct).
All that, plus I think it’s not the best graphical representation of the modulo concept. I don’t know what would be, but I would think of something that wraps around…
update: how about a level where you get killed, unless you wrap around using modulo – e.g. yaks standing in a zig-zag pattern?