From Reddit correspondent Oelund, we have this slow motion footage of M1 Thumb. No, I will not be doing my own version of this video. :)
When closing an M1 bolt, always make sure to hold the bolt handle while pushing the follower down. The "official" way to do this is to use the right hand, and hold the handle back with the heel of the hand (fingers pointing down towards the ground) while using the right thumb to depress the follower. When in doubt, point your thumb towards the muzzle, as this will tend to make the bolt push your thumb up out of the action. If you grab the gun around the chamber and point your thumb towards the rear sight, you are much more likely to get it squished.
Other rifles can also do this, most notably the Ljungman and Hakim - as they do not have handles directly connected to the bolt to hold onto and they have a rather unusual action that most people will not be immediately familiar with.