At noon, ten kilometers from their destination, Aymo's cars gets stuck in the muddy road. Henry orders the two engineering sergeants to help free the vehicle. Fearful that they will all be overtaken by the enemy, the sergeants refuse, and run. Henry pulls his pistol and shoots one of them, injuring him. The other escapes. Bonello then takes Henry's gun and finishes off the injured sergeant with a bullet to the head.
The chaos of the retreat has caused the drivers to do whatever it takes to get to their destination. Within this context, Henry is just doing his duty as an army lieutenant—he is forcing men who don't want to engage in battle to either fight or die.
Henry puts the coat and cape of the dead sergeant under the wheels of the car to help it escape from its rut, but it doesn't work. As they walk away, Bonello, who is a Socialist, says that he has always wanted to kill a sergeant.