A few months ago I was just about to leave the house and couldn't find the front door key, after searching everywhere I gave up and took 'the spare'.
The lost key didn't re-appear until weeks later, where it sat very obviously in the middle of my empty table - I can't figure out how it got there on its own, and really wonder if there is a mischievous house poltergeist playing games...
What to buy for 18th birthdays?