Little Johnny and his friend Billy were on their very
first train ride, with Billy's mother.

A vendor came down the corridor selling a candy
bar that neither had ever seen before. Billy's mom
bought each one of them a bar.

Little Johnny eagerly tore open the wrapper and bit
a bit off into his mouth just as the train went into
a tunnel. When the train emerged from the tunnel,
he looked across at Billy and said: "I wouldn't eat
that if I were you."

"Why not?" asked Billy.

Little Johnny replied, "I took one bite and went blind
for half a minute."