1. You wake up suddenly in the middle of the night to see them standing motionless in your doorway. Sure, they might claim to just be thirsty or scared of a thunderstorm, but I think we all know the truth.
2. You've caught them pushing buttons on the remote until they manage to play past episodes of "Dexter" on Netflix.
3. The level of satisfaction they feel in pulverizing blackberries into pulp is slightly disturbing.
4. Every time they "help" you set the table, they always seem to find a steak knife rather than a baby spoon.
5. Action figures and LEGO guys are often found decapitated or otherwise dismembered at cleanup time.
6. Every time you take a shower, you keep one eye peeled for the door to slowwwwly inch open.
7. Despite your warnings that they are not allowed to touch your Elf on the Shelf, lest his magic disappear, you frequently find Frank (or Fluffy, Giggles, Buddy, Captain Sparklebuns or whatever ridiculous name you gave the thing) in horrifying circumstances.
8. They get a little overzealous in their lightsaber play, someone loses a limb and they just bust out in maniacal laughter.
9. They turn helpless, woodland creatures into hats.