In addition to being one of the most famous U.S. military small arms of all time, the venerable M1 Garand rifle is also the subject of much misinformation, "urban legends" and sheer fantasy. I have written many times before about the absurdity of the claim that the "ping" sound of the ejected M1 clip was some sort of deadly defect because it altered the enemy that the rifle was empty and the hapless soldier could be killed with impunity before he could reload. I'm not going to recite the reasons why this is implausible again as it has been cited in some of the older postings here.
However, another topic that seems to be repeated with increasing frequency on some of the internet sites today is that of the dreaded "M1 Thumb." This is the result of the bolt slamming on a thumb that has been inserted into the magazine. It can definitely happen and is not a pleasant experience. The result is a bit painful and can result in a bruised thumbnail. It is often inferred that this can result anytime a clip is inserted into the rifle. Actually, it can't. When loading a full clip, it is not possible for the bolt to close on the thumb because eight cartridges are blocking it until the clip is fully seated. Under the right circumstances, a slight pinch might occur but will not result in a painful bruised thumb and is very rarely a problem. The real culprit of the M1 Thumb is when someone attempts to close the bolt on an empty rifle by pressing down on the follower and trying to quickly remove the thumb before the bolt slams shut. I can testify from experience that this is asking for trouble. One of first times I handled a M1 rifle many years ago, I tried this and did indeed suffer a M1 Thumb. I quickly learned that by holding back the bolt with the heel of the hand when depressing the follower while moving the hand forward to allow the bolt the slowly close on the empty magazine, the entire unpleasantness can be avoided.
Yes, the M1 Thumb is real but it is actually the result of incorrect handling of the rifle. It won't occur during normal loading.