Occasionally passengers do not heed the advise in the pre-flight briefing, and put their arms up on the combing. With occasionally eye-popping results!
Be sure to keep the canopy closed people! It is completely harmless if it does open - except for perhaps requiring a change of underwear from the extra dose of in flight adrenalin rush.
In summer we regularly fly with canopies open, it is windy, loud, but on a 38°C day very refreshing!