What are the lista of things tu can do with a stop-watch? lol

In season 1, episode 8, "They keep killing Suzie", at the end of the episode Ianto dicho "There's a lot of things tu can do with a stop-watch.", probably sexual things because of the looks he and Jack shared.
I was just wondering exactly WHAT can tu do with a stop-watch. Even my sick mind couldn't figure THAT out.
Do tu have any idea? XD