From the time Melquiades' gun is fired and then he's killed; the scenario takes much longer when shown the first time, from Norton's point-of-view.
When Norton is reading the Hustler alone and hears gunshots, he runs back to the truck to get his gun, his trousers are unbuckled and keep on falling. He gets into the truck, grabs the guns without buckling his trousers, gets out and starts running to fire at Melquiades, but now his trousers are buckled and don't fall down.
At 1:51:24, when Pete stands on a hill overlooking the captive sitting in the bushes, his hat is a wide brim sombrero; it's usually a conventional straw Stetson.
The alcohol given to Mike Norton by the Mexican bear hunters is caramel colored. Later, after the third burial, the alcohol is now dark brown.
When Norton is heading out on a solo patrol before encountering Melquiades, he drives briskly through the countryside without wearing his seatbelt. When he stops the car to get out, he unclips his seatbelt.
When Pete buys two beers and asks for directions in a Mexican store, the Mexican guy in the store is drinking an orange Topo Chico soft drink. The Topo Chico brand doesn't come in orange flavor in Mexico, only in the USA.
When Pete and Mike are in the ruins at Jiminez, a crew member can be clearly seen crouching in a corner as the camera pans past him.
Just after Pete describes the Melquiades house at the end of the movie, there seems to be some sort of crew member visible starting in the lower left-hand corner of the screen.
After the hotel scene, when Pete and Melquiades Estrada drop the girls off at their vehicle, Melquiades Estrada gets back in the truck and puts the window up, a crew member can be seen in the reflection of the window.
Near the end of the movie while at Jimenez Tommy Lee Jones walks past a rock wall, a crew member is clearly visible in the middle of the frame squatting next to the wall.
The story takes place in the Big Bend area of Texas but there is a banner in the restaurant for the Van Horn Lion's Club. Van Horn is a long way from the Big Bend.
After Pete exits the hospital where Mel's body was taken, the sign says Cibola County General Hospital. There is a Cibola County (Grants), New Mexico, but none in Texas. Cibola County, NM is about 450 NNW of the movie setting.