After the majority had gone we were left standing with him. He noticed that my shoe was very misshapen. The heel was so twisted it was facing forward. The Rebbe said, "Your shoe has got a face like a slap in the face." Then he was silent for a bit. We certainly believed that nothing he said was simple and all his words contained deep secrets.
He then said: "Our casual talk!"- stressing the word our. "Let some mystic tell me how that comment contains all the mystical intentions of circumcision as well as what is higher than mystical intentions."
With awesome grace and holiness the words began to flow forth from his lips. "There are cases where they slap a person in the face, others where they slap him on the sandal." The Rebbe mentioned the statement of the Rabbis referring to a sandal: "A man should not marry his friend's widow if she is carrying. This is a decree to prevent the embryo from developing a face like a shapeless sandal." He also mentioned other statements of the Rabbis involving the concept of sandals. All these statements point to how the concept of the sandal contains deep Torah secrets.
He then gave over the entire lesson. None of us yet knows how far it reaches. Everything was presented allusively in a succession of flashing sparks. May God grant us the merit of understanding all of this completely.