[PW] Meaning of Shakespeare quote: Puck: "Now to scrape the serpent's tongue"

[Dianne]

A middle school teacher would like to know this one:
  
"In Puck's final monolog from Midsummer Night's Dream: 
What is the meaning of the phrase  'Now to scrape the serpent's tongue'?"
   
  I'm not having much luck trying to decipher it.
   
  Many thanks.
   
  Dianne Parham
  San Diego State University
  Liberal Studies Program
  (retired from San Diegp Public Library)