@TobyBartels

Interesting! Thanks.

"Snick snack" is new to me, and is very similar to the sound made by the vorpal blade in Jabberwocky. Unfortunate accident, surely, on Lewis Carroll's part?

@Catvalente

@CppGuy
According to Wikipedia, it was published in an academic book in 1841, which gives Carroll plenty of time to read it before he publishes Through the Looking Glass in 1871. Although since ‘tokl tobl’ also works as onomatopoeia, it might have taken a while for people to think of applying the substitution cipher to it; I don't know what the 1841 book says about it.

It's conceivable, since the phrase was in use in the 15th century, that it was continually in use through the 19th century, but if so then it wasn't in print. (The OED dates ‘snick-snack’ to 1925 and ‘snicker-snack’ to 1871, with Carroll. Note that the OED doesn't seem to consider Flees Flies and Friars, which is more than half in Latin, to be an English source; it dates ‘fuck’ only to 1513.)