Why is it that you get static electric shocks off supermarket trolleys?
Some shops are worse than others.
I know that there is a lot of electric being used in these places and maybe the electrical magnetic field is the culprit.
Another tip is to hold a finger about 1mm from your wife's earlobe while you reach for the trolley with the other hand. It doesn't stop the shocks, but it makes it more amusing. (And yes, I do speak from experience).