Bobo The Great

Except if you are the overeating type of depressed person.

Ever spilled a drop of diesel? Exactly that happens

To be fair, a metal subway car (provided they removed every piece of rubber, plastic and electronic component) is environmental quite neutral, as metal and glass are inert. In this case though, I’m pretty sure tennis ball contain plastic so it wouldn’t be whise to just leave them in the open. If they were glass balls, it would be better.