Bear scratching head well! (3)
I believe the answer is:
ooh
'well' is the definition.
(both are exclamations expressing surprise)
'bear scratching head' is the wordplay.
'bear' becomes 'pooh' (Winnie the Pooh).
'scratching head' means to remove the first letter.
'pooh' with its first letter taken away is 'OOH'.
(Other definitions for ooh that I've seen before include "sound excited" , "Exclamation of delight" , "Expression of surprise" , "My goodness!" , "Exclamation of surprise or pain" .)