This video discusses Case 2 of the Gateless Gate. (The koan is written here below if it is unfamiliar of for interest as the video does not recite the it..)
Whenever Hyakujō delivered a sermon, a certain old man was always there listening to it together with the monks; when they left the Hall, he left also. One day, however, he remained behind, and Hyakujō said to him, “Who may you be?” The old man replied, ” I am not a human being. In the far distant past, in the time of Kashō Buddha, I was the head monk here. On one occasion a certain monk asked me whether an enlightened person fell into cause and effect, and I answered that they did not. Thus for five hundred lifetimes I have been reborn a fox. I now beg you to release me from these rebirths with a turning word.”
He then asked Hyakujō, “Can an enlightened person fall into cause and effect or not?” Hyakujō answered, “cause and effect is not obscured.” The old man made his bows, he said, “I am now released from rebirth as a fox and my body will be found on the other side of this mountain. I wish to make a request of you. Please bury me as a dead monk.”
Hyakujō had the karmadana, or deacon, beat the clapper and informed the monks that after the midday meal there would be a funeral service for a dead monk. The monks thought this was odd, as all were in good health, nobody was in the hospital, and they wondered what the reason could be for this order. After they had eaten, Hyakujō led them to the foot of a rock on the farther side of the mountain, and with his staff poked out the dead body of a fox and had it cremated as a deceased monk.
In the evening Hyakujō ascended the rostrum in the Hall and told the monks the whole story. Ōbaku asked: “This old man made a mistake in his answer, and suffered rebirth as a fox for five hundred lifetimes. But suppose every time he answered he had not made a mistake, what would have happened then?” Hyakujō replied, “Just come here to me, and I’ll tell you the answer!” Ōbaku then went up to Hyakujō ̶ and boxed his ears. Hyakujō, clapping his hands and laughing, exclaimed, “I thought the barbarian had a red beard, but here is a red bearded barbarian