A brunette is standing on some train tracks, jumping from rail to rail, saying "21" "21" "21". A Blonde walks up, sees her and decides to join her.
She also starts jumping from rail to rail, saying "21" "21" "21". Suddenly, the brunette hears a train whistle, and she jumps off the tracks just as the Blonde is splattered all over the place.
The brunette goes back to jumping from rail to rail, counting, 22" "22" "22".