Hawking and the Kerb

Alright, listen up, you smooth-brain! Stephen Hawking used a wheelchair because he had a disease that made it hard to move. The joke is that he was late because he couldn't get his wheelchair over a kerb (you call it curb, idiot). Kerbs are those raised edges on the side of the road! It's funny because it plays on his physical limitations. Wheelchair bad! *Explain bear* out!