Comic book art is usually drawn in pencil by one guy and then, after the page is lettered, the work is "inked" by another. The inker interprets and embellishes…and since it's his linework that gets reproduced in the finished publication, he can go a long way towards improving or ruining or just preserving what the pencil artist did. Throughout his career, the late, great Jack Kirby had his penciled pages inked by a wide range of great talents and a few of the lesser variety. The efforts of one inker, Vince Colletta, remain especially controversial, long after the work was done and both men have passed on.
To be fair, Colletta has his fans and his work was loved by many readers of the day. But some of the artists whose work he inked felt he had minimal talent and all felt he expended minimal effort. (Again, to be fair, he was often paid minimal money — but so were a lot of guys who put in more time.)
One of the big complaints about Colletta was that he would simply leave things out. The panel above, which was scanned from a piece of Kirby/Colletta original art for Fantastic Four #40, gives us an example. If you click on it and enlarge the image, you'll see that Jack drew in a figure of Mr. Fantastic that Vince and/or his staff of lowly-paid assistants just ignored. I've occasionally seen inkers do this for creative reasons because they felt it improved the composition, but Colletta tended to decide this any time a page took him more than about 90 minutes.
Anyway, folks sometimes ask me why so many artists disliked Colletta's inking and there's one of the reasons. Thanks to Tom Field for the scan, and to Glen Gold who first noticed this omission.