I found this series of photos in an old issue of Life
Magazine (Dec. 7, 1936). It was titled "Tricks of Paris Season" and had this caption:
Patrons of a Paris nightclub are being entertained with this spectacle of one man swallowing another's head. M. Nicol pries open M. Martin's mouth, lowers his head, rams it in until the spectators see it disappear. Only the cold sober feel cheated by this act.
I assume the method of the trick is obvious enough not to require explanation.
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