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L. Frank Baum's early Oz stories contain an amazing quantity of removable heads. Here are a few examples, off the top of my head...
In
Wonderful Wizard, the Scarecrow's head is removed in order to put his new brains in the right place - and of course, the Wizard appears to Dorothy as a giant head!
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In
Marvelous Land, Jack Pumpkinhead loses his head a few times, and is constantly worried whether it might spoil.
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In
Ozma, Princess Langwidere has a head for every day of the month and threatens Dorothy with a head exchange.
Road to Oz introduces the Scoodlers, who throw their heads at their enemies. Also, Button Bright and The Shaggy Man are given replacement fox and donkey heads for a while.
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In
Emerald City, one of the groups of villains are the Whimsies, who wear large cardboard heads over their own tiny heads.
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The theme pops up in non-Oz stories as well - in
A New Wonderland, the King of Phunniland loses his head and is forced to try new heads of various materials before regaining his original.
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In
John Dough, the General who goes to pieces lost his head at Santiago and had it replaced with wax - but the female executioner is stymied when she is unable to cut the head from a wooden cigar store Indian.
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One of the most memorable moments in the series is the discovery by the Tin Woodman of his former head, in a cupboard, in
The Tin Woodman of Oz. The Tin Woodman was originally made of flesh and bone, but slowly cut himself to pieces with an enchanted ax, visiting a local tinsmith after every accident to replace each missing part. The tinsmith kept all the pieces, and when a similar fate befell another character, a soldier, the tinsmith used the various body pieces of both men to create a new man. Since he only needed one head, the spare was kept in a cupboard in his shop. This whole concept is very intriguing.