The notion that magpies steal shiny objects is ancient and widespread

On a sunny evening recently my son and his housemates decided to have a barbecue in their back garden. 

My son left his keys out on a table in the garden overnight and when he went to collect them the next morning they were gone.

An exhaustive search failed to find them and they sat down to try and solve the mystery. There is a high block wall all around the garden. His car key was on the ring but the car was still parked outside so it was unlikely that a human thief had scaled the wall. Using the Sherlock Holmes doctrine that you eliminate the impossible and what remains, however improbable, is the truth, the blame was laid on the particularly large magpie that included their back garden in his territory.