"Who breaks a butterfly upon a wheel" is a quotation - sometimes misquoted with "on" in place of "upon" - from Alexander Pope's "Epistle to Dr Arbuthnot" of January 1735. The line has entered common use and has become associated with more recent figures.
The trivia item below may give away important plot points.
When Neil opens the poetry volume, you can see the lines 304 to 310 of Alexander Pope's "Epistle to Dr. Arbuthnot": But all such babbling blockheads in his stead Let Sporus tremble - A. "What? that thing of silk, Sporus, that mere white curd of ass's milk? Satire or sense, alas! can Sporus feel? Who breaks a butterfly upon a wheel?" P. Yet let me flap this bug with gilded wings, This painted child of dirt that stinks and stings, On top of the page there is merely a title "Satires", because the 'Epistle to Dr. Arbuthnot' is also known as 'Prologue to the Satires'. Notice that in the final scene, Abby seems to continue Pope's rhyme by saying: "Who breaks a butterfly on a wheel? I do, Neil."