The Collaborative International Dictionary of English v.0.48:

Unpick \Un*pick\, v. t. [1st pref. un- (intensive) + pick.]
   To pick out; to undo by picking.
   [1913 Webster]

WordNet (r) 3.0 (2006):

unpick
    v 1: become or cause to become undone by separating the fibers
         or threads of; "unravel the thread" [syn: unravel,
         unknot, unscramble, untangle, unpick] [ant: knot,
         ravel, tangle]
    2: undo (the stitches) of (a piece of sewing)