It was the shot heard 'round the Twitter world. Invited to join new host Jimmy Fallon on "The Tonight Show," Chicago Mayor Rahm Emanuel responded over Twitter, saying he'd join Fallon on-air if the late night jokester agreed to take part in the annual Polar Plunge. Fallon thought about it a bit, perhaps reluctant to spend a weekend sprinting into Lake Michigan during one of the worst winters in Chicago's infamous winter history, and finally agreed.

Fallon took the plunge Sunday amid single digit temps. Welcome to Chicago, Jimmy.