Howard Hawks's slapstick treatment of the Jekyll-and-Hyde mad scientist, in particular Rouben Mamoulian's reverse-evolutionary version of him in 1932, where Hyde was explicitly linked to the apes. Here an elixir of youth -- perfected by a laboratory chimp! -- transports its imbibers back to adolescence and all the way to infancy. A pleasing balance of silliness and significance, and very enthusiastically played by Cary Grant as an absent-minded professor awakened to a midlife crisis. With Ginger Rogers, Charles Coburn, Hugh Marlowe, and Marilyn Monroe. (1952) — Duncan Shepherd
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