Two stars of the long-running TV show “Whose Line Is It Anyway?” are appearing in Des Moines tonight to demonstrate their skills at improvisation. Using their quick wits, Colin Mochrie and Brad Sherwood will take suggestions from the audience to create original scenes, pulling audience members onstage to take part. Mochrie describes a little of what will happen on stage, but he can’t go into much detail since nothing is rehearsed.Mochrie says he’s gotten used to -not- using a script. He says “The scariest part for me is five minutes before the show when I realize I’m heading out there with absolutely nothing and these people have paid for entertainment. But once I’m on stage, it’s just a lot of fun.” Mochrie, a 46-year-old Canadian, says in real life he’s not very bright or quick but getting under the lights blinds all of his inhibitions, he accepts the ridiculous premises and simply runs with whatever goof-ball ideas are suggested. Mochrie and Sherwood perform tonight at the Civic Center of Greater Des Moines. The show is taking them all over the U.S. — in the past week, they’ve also performed in Texas, Alaska and Pennsylvania.