The sheer number of would-be joke writers within its walls tells you that it's relatively easy to fire out a few one liners in the safe environment of Twitter. But arguably Twitter's cosy bosom is no place to prepare yourself for the bear-pit of live performance. If a joke falls flat on Twitter it will simply get washed away in the ceaseless stream of the timeline. No one boos. No one gets up and walks out. The long, deathly silence which must haunt the dreams of every stand-up comedian is of no concern.