One day, a teacher took his pupils to a chicken farm to pay a visit. When they came near the incubator, a chick just got out of its eggshell.
"It's wonderful to see a little thing come our from the eggshell, Isn't it?" the teacher said.
"Yes, sir." said one of the boys, "but it would be more wonderful if we knew that how a chick gets into its eggshell before hand."