Ramban, on Gen 27:12

“If my father shall feel me, and perceive it, I fear lest he will think I would have mocked him, and I shall bring upon me a curse instead of a blessing.”

“PERHAPS MY FATHER WILL FEEL ME. The reason that Isaac will feel him is not for the purpose of recognition. Instead, Jacob said, “Perhaps he will bring me near him to kiss me or to put his hand on my face in the manner of a father demonstrating affection for his son, and in feeling me he will discover that I am smooth.” Now I wonder why Jacob was not afraid of vocal recognition for all people are recognizable by their voice as our Rabbis have said, “How is a blind man permitted to live with his wife? And how are people permitted to live with their wives at nighttime? Only by vocal recognition.” Now if ordinary people have such power of recognition, what of Isaac, who was wise and expert in distinguishing between his sons? He should truly have the power of recognition by voice. Perhaps the brothers had similar voices, and therefore the Sages said that the verse, The voice is the voice of Jacob, refers not to Jacob’s voice but to his words, i.e., that he speaks gentle language and mentions the Name of Heaven., as referring to the kind of language Jacob used. It may be that he altered his voice in order to speak as his brother did, for there are people who know how to do this.”

Imported from an open dataset — not yet checked against the printed edition.