When we did test runs before DH woke up, my MIL was worried about the loud "pop" sound that the balloon made and thought it would tip him off that something was up. However I was right instead, he was in too much of a panic, his brain didn't even register the popping sound.
And I don't think it's so evil, labor actually COULD begin with my water breaking like that, it's good for DH to think about NOT panicking if it does. And now I know how little he knows about labor starting that way. He thought things would start right away and the baby would just whoosh out of me at any second. I had the hardest time not cracking up when he asked what we needed to do, and the look of alarm on his face when he thought I should move to the bedroom, like I wouldn't make it down the hall in time!

Think of it as a training experience, not a prank. Hubby needs a few simulated "what if" situations.
