The Collaborative International Dictionary of English v.0.48:

Snarl \Snarl\, v. t. [imp. & p. p. Snarled; p. pr. & vvb. n.
   Snarling.] [Etymol. uncertain.]
   To form raised work upon the outer surface of (thin metal
   ware) by the repercussion of a snarling iron upon the inner
   surface.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Snarling \Snarl"ing\,
   a. & n. from Snarl, v.
   [1913 Webster]

   Snarling iron, a tool with a long beak, used in the process
      of snarling. When one end is held in a vise, and the shank
      is struck with a hammer, the repercussion of the other
      end, or beak, within the article worked upon gives the
      requisite blow for producing raised work. See 1st Snarl.
      [1913 Webster]