Ask HN: hacking a non-computer system (YC application question)?

I'm struggling with the following question for my YC application:

'Please tell us about the time you, dirkdeman, most successfully hacked some (non-computer) system to your advantage.'

It must be the language barrier, but I have no grasp of the meaning of 'hacking a non-computer system'. What does this mean? A 'system' like taxes, governement, school or a company you work for? Or is it something more trivial, like making a beer cooler out of Lego? Does anyone has an example of this to put me in the right direction?