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An early application of homophones for magical purposes is Stanley Collins's “Whisper-word”, marketed in 1931 by Goldston. This was a divination of one word chosen by one person from five words chosen by another. Each word was written on a separate card by a third person. The words are selected from two printed lists that are checked verbally, proving to be identical. Actually, the lists are comprised of homophones, one set spelling with one more letter than the other, thus providing the clue for the divination. See pp. 209-210 of Stanley Collins: Conjurer, Collector, and Iconoclast by Dawes.