There's really no sure way to know.
Why is Santa so jolly? Because he knows where all the naughty girls live. Happy Holidays Fun!
An engi-near!
The answer may shock you.
None if nobody's looking.
A: Only one but he'll tell everybody.
2...and don't ask me how they got in there. (My 87 year old grandma just told me this one)
Someone who lies awake at night wondering if there's a dog
Someone who stays up at night wondering if there really is a dog.