They call him Stumpy. Not his mum, she calls him by his real name, Ryan, but the others call him Stumpy. Nobody remembers where the name came from. It’s not as if he’s particularly short and he has all his limbs intact. The name seems to have grown around him and there it is.
His limbs are intact but his mind, well his mind is a different thing. If the kids who teased him had possessed a modicum of intelligence it could have been that they realised his brain is stumped but that’s probably a bridge too far for them.

