Eggcorn Forum

Dixon’s break your piggy bank catch reminded me of this long-time favorite of mine:

[to waiter:] Could I have a piggy-bag to take that home in?

Either the picture of the pig waiting at home for the left-overs, or the diner himself as the pig, works for me. It’s a blend, and not an eggcorn: piggy and doggy sound and look too different for eggcorn status.
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There are quite a few hits with piggy bag substituting for piggy-back. E.g.:

to piggy bag the development board onto another board (in case of development kit the SC14CVMDECT_DB is piggy bagged …

reducing the amount of rich snippets appearing in search results by 15% to combat the rise in black hat tactics that piggy-bag on authorship.

These could be construed, I suppose, to involve carrying the piggy-backed object in a bag, whether on the back or not, and might be eggcornish to that extent. I don’t know if the perps do this or not.
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Piggy-back is apparently about four centuries old. Perhaps it is a folk-etymologic corruption of pick-a-back , which itself may be from pick-pack , or maybe not. This would be a folk-etymology that we would probably deny eggcorn status to on the grounds of it lacking sense: what have pigs got to do with anything? I as a kid tried to picture carrying a pig that way (on my back, with my arms under its legs), but the mind boggled, as they say. No self-respecting pig would put up with it!