Two Welsh guys were taking their first train trip. They opened their lunch boxes and both took out bananas, which they'd never seen before.
The first one eagerly peeled the banana and bit into it just as the train went into a tunnel. When the train emerged from the tunnel, he looked across to his friend and said, "I wouldn't eat that if I were you."
"Why not?"
"I took one bite and went blind for half a minute."