A monk was asked to discard everything.
“But I have nothing,” he exclaimed.
“Discard that too!” ordered his master.
(Swati Chopra, in Buddhism – The sound of one hand clapping)
Katsu! According to Swati Chopra’s article, “Rinzai was also famous for shouting Katsu!, a nonsensical word, as an answer to koans.”
Thanks to Babaloo Bonzai and Babaloo Bonzai’s Zen Soup for providing the link to this material.