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"?