I was doing a trick where you turn the bottom card of the deck over so that it looks to be the top from both sides.
Fan out the cards and let them pick one, not showing the bottom is turned over.
Now the actual trick is...
Then whilst you tell them to look at the card and memorise it you sneakily turn the pack over, they slip it back in.. and now it's magically the wrong way up
BUT
This person was wearing reflective sunglasses, and the car window behind them was also reflecting the card in their hand.
I was able to read the cards without putting it back in the deck...
MAGIC!