What can go up a chimney when down,but cannot go down a chimney when up ?
Smoke!
Sorry, but not the answer I'm looking for. Give it another guess.
Lol. But you gotta admit Lou, my answer does make sense...."smoke, if its down, can only go up. And If smoke is already up in the air, it doesn't go down.
But let me think a bit...and see if I can't get it, lol