Near the end of the film, the Indian that Sgt. Jonas kills on the wagon changes position from lying on his back to lying on his front when the wagon is turning round, to lying on his back again.
Right around 39:04 , as the two horses pull away, one of them raises his tail and loudly passes gas. It can be clearly heard on the film's audio.
Capt. Santley, sending a message to the General, orders Pvt. Cassidy to "step on it". This phrase, meaning to go fast, came from accelerator pedals in automobiles and pressing down to go faster. It would not have been a phrase used in the Wild West.
As the two troopers are being buried, the reflection of the key lighting is clearly visible in the bugle.