Have you ever, by accident or on purpose, found out a Christmas present someone had bought for you before they gave it to you? Maybe you stumbled across a receipt, overheard a phone call, or opened a package received in the mail and found out what the present was?
I did happen to stumble across one or two accidentally a few weeks ago myself, but I forgot what they were. I didn't see the actual presents, but I found the same thing in a store and was going to buy, only to be told I couldn't do that.