"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.
This is the second time that Pierce Brosnan and Gerard Butler have appeared in a movie together. The first was actually Tomorrow Never Dies (1997) where Butler played one of the crew on the HMS Devonshire, and Brosnan of course played James Bond. However, their characters in that film had no interaction.
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 ...