No, it's not a geometry question. It's not even what actors sometimes whisper onstage. It's a TV show from a coupla generations ago. (The question could be expanded to "What's My Line of Work?"). A mystery guest would appear on the show, signing their name so that only the audience could know who they were. If the guest's face was known to the four judges working on the show, the judges' eyes would be covered with a mask. The judges would then ask yes/no questions of the guest, trying to guess "What's my line?" The guests ranged from a ≈80-year-old woman who caught shoplifters to well-known movie stars. The guests sometimes went to great pains to disguise their voices, and that's where some of the hilarity comes in. Sometimes their antics caused even the host to crack up! That's when you knew you had a real winner on your hands. Late last year while studying for my biochemistry final, my brain fried. I decided that it was time to cool the sizzling mess with an administration of YouTube. And it worked. I found What's My Line and had a blast. (Hold it -- maybe that was a different time. I forget!) Anyway, in case you're wanting to serve yourself up some laughs, here's some of the laughingest guests (at least of the episodes that I saw!):
Colonel Sanders (His face hadn't yet become the icon that it is now; they didn't even the judges wear masks!)
Groucho Marx (Groucho as Groucho. Hard to beat)
Sammy Davis Jr. (Had an amazing repertoire of voices!)
Art Carney (My personal favorite; so humble, and so talented)
Ed Sullivan (This guy's a riot!)
Two other memorable episodes that I saw was 1) when one of the judges' fathers came onto the show, and 2) the last episode.
You can see the full listing of guests at (of course) Wikipedia.
(By the way, am I right in thinking that this show is what the villians were watching in the cartoon version of One Hundred and One Dalmations?)