1926 Neck detail
I have highlighted the area at the chin and neck. I put several of these "spurs" on the coin forums quite a few years ago and the consensus was they are spurs. I disagree and believe they are actually caused by die-clash. If you look at the shape of the highlighted area, it closely mimics the shape of these "spurs".
1924 dieclash
This 1924 example show the "spur" on the second N in PENNY, where they all seem to occur, but also shows the outline of the facial features. This is a die-clash in my opinion. Some of the "spurs" show on the N but no facial features are apparent, and there are some multiples following.