A difficult visual puzzle

Discover magazine includes puzzles in each issue. The image above is particularly challenging. Here's the accompanying text:

In Petroski's The Pencil (Knopf, 1990), he reports that in 1981 the Engineering News-Record printed a large, colorful drawing of a pencil on its cover. Unfortunately the drawing contained several errors, which the readers gleefully pointed out in a deluge of mail. Here is a modified version of that drawing. Can you spot four errors? Assume you are looking at a typical number 2 pencil directly from the side.

Since I don't know how to paste an image into the comments section, I'll send you to this link to view the answer.