A couple of years ago, I replaced 1 piece of my wife's nativity every day with kid's toys and took pictures to send to my friend until one day...

I hear her freaking out about it and yelling at the kids. The kids had no idea this was going on and didn't know where the pieces I had replaced had gone. My wife was convinced the kids (5/7 at the time) had been the ones to do it and was demanding they go search their rooms until they find the missing pieces. I was working upstairs and heard this going on but didn't quite process what it was about for a couple of minutes. Then I fessed up and returned the the pieces I had replaced. Turns out she was upset because the set was a gift to her from my grandmother who had passed a few years earlier (and they got along really well) and she was worried pieces had been lost or broken.

Here's the last pic I got before it was discovered.