While meditating in his room, a student thought he saw a spider moving on the ceiling and descending above his head. Each day, the spider returned while the student meditated, growing larger and more menacing each time. The student became frightened and decided to talk to his master about this.
He told his master that he plans to take a stone, or a thick book with him during meditation, so that when the spider dangled above his head, as it unfailingly did, he would kill it.
The master, however, came up with another idea. He told the student to bring a piece of chalk with him, and when the spider appeared he should mark an X on its belly.
Baffled, the student returned to his room with a piece of chalk. He started meditating, and when the spider appeared, swallowing his disgust and fear, he reached for the spider and drew an X on its belly. Then he went back to the master.
The master told the student to lift his shirt and look at his belly. There was X written in chalk there.