Etymology as requested

Chewing the Rag --

Sometimes credited to Civil War army slang. Also may be of the Victorian era and "chewing the rag or fat" was derived from the ladies in a sewing circle and using there tongues to chew the (rag) their cloth, or (fat) a juicy morsel of gossip.

...http://archiver.rootsweb.com/th/read/WORDS/1998-05/0896378654

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Piggyback --

Piggyback, the main sense of which is '(of something carried, esp. a person) carried on the back or shoulders', dates back to the sixteenth century, but is found in many different forms.

The earliest forms vary widely: pickback, a pickback, a pick pack, on pick pack, and pick-a-pack were all in use before 1700. The usual assumption is that the pick word is a dialectal word for 'to throw' that is related to the standard word "pitch."

The second element is probably back, in reference to where the burden is carried. It could also be pack, which was the more common form in the seventeenth century. So the compound could refer to "a pack pitched (onto one's back)," or "(a burden) pitched on one's back."

The alteration to piggyback is an illustration of folk etymology.

Folk etymology is the process of altering an uncommon word or element to conform it to one that's better known. Pickback, which had become obscure, was changed in the eighteenth century to pig back; this was in turn changed (perhaps influenced by the pick-a-back form) to the familiar piggyback in the nineteenth century.

So while pickback definitely doesn't make any sense, piggyback at least seems as if it could.

Since the word had so many variant forms even in its early history, the one thing we can conclude for sure is that people interpreted it in many different ways as soon as it appeared, and this same reanalysis is the source of our current word.

...http://www.randomhouse.com/wotd/index.pperl?date=19960816