This was a story told to us by our chemistry master at school. A student wished to make some potassium hydroxide solution (aqueous) and decided to throw a large lump of potassium into a bucket of water.
Out of the corner of his eye, the professor observed what the student was about to do and hurried over. After confirming this was what was intended, he asked the student to first to stir the water in the bucket for five minutes before adding the potassium.
Puzzled, the student followed after him to ask the purpose of this action.
"It will give me time to run away," said the professor.