In Reply to: At it like knives posted by Jim Stuart on December 04, 2009 at 09:02:
: My Grandmother, an English Victorian lady of some substance, used the phrase "At it like knives" of anyone involved in some (disreputable) conduct. The thieving postmen, the swindling market traders, the young kids today were all "at it like knives". It is hence a well known phase in our family and not unknown outside of it. So, what were "knives" doing, with such apparent abandon, to prompt Victorians and maybe their predecessors too, to preserve the memory of their activity in this way. Might one suppose that the "Knives" may have been "Knaves"?
I've only ever heard "going/being at it like knives" used to mean "having vigorous sexual intercourse", and my guess is that the reference is to knife-grinding. Before the introduction of stainless steel kitchen knives, itinerant knife-grinders would walk city streets crying "Knives to grind!" and householders would bring blunt knives out to be ground sharp there in the street. So the brisk back-and-forth motion of knife-grinding was familiar to all and available as a metaphor for sex - indeed in slang "to grind" meant precisely that from the 17th through the 19th centuries.
My guess is that your respected grandmother heard this naughty phrase used and misapplied it because she was simply too virtuous to know what it meant, like poor Robert Browning using "twat" in "Pippa Passes".