The gates to Heaven and Hell are guarded by identical looking angels.
One always tells the truth, the heaven one, and one always lies, the beastly Hell one.
You must decide which portal to pass through.
You are allowed only one question, which you may ask of either of the guardian angels.
How can you be sure of passing through the portal of your choice?
Update: Old Knudsen has cleverly reminded me. The angels sometimes swop doors when they get a bit bored.
You know the kind of thing. All doormen do it. This often weeds out the fly men who turn up still wearing their bunnets! Put that in yer ectoplasm and smoke it Knudsen.
Late Update: We have a WINNER!
Tattieheid! Well done that man! First rate!
And my goodness Kav was touching the prize too. What clever people there are round here.