Rail Jumping

A brunnette 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 brunnette hears a train whistle and jumps off the tracks just as the Blonde is splattered all over the place.

The Brunnette goes back to jumping from rail to rail , counting "22" "22" "22".