Leading up to the argument that sparks the Del Mar divorce (finalized on 6 November 1975), Ennis is on the couch watching Kojak on a Saturday night. Kojak didn't air on Saturday nights until its 5th season, 1977-8.
Ennis gets a postcard from Jack which reads, "Ennis, see you in a couple weeks, fish should be jumping. Jack." The postmark is Childress, Texas, July 1972. A couple of weeks later, Jack is driving a blue Ford truck with a 1976-7 grill.
When Ennis was driving Alma Jr. home from the bar where Alma and his waitress girlfriend have met, along the path in the background, next to the Dodge Neon, is a RV or trailer car. These had not been introduced yet.
The two teams playing football on TV during the Thanksgiving Day dinner are the CFLs Edmonton Eskimos and Montreal Allouttes. Obtaining the rights to NFL footage is very expensive for just a few seconds of background footage.
When Alma & Ennis are in the kitchen at Thanksgiving, there is a plastic strainer thing that goes over the sink which wasn't commonly available until the advent of dollar stores in the 1980s. Is there also a salad spinner on the counter? That would have been quite rare in the 1970s as well.
The first reunion of Jack and Ennis is on 24th September 1967. On the next day 25th, they went onto the mountains and at that night there was a full moon. However, the full moon of September 1967 should be at 18th day, not 24th or 25th.
During the scene in the supermarket where Alma works in the 1960s, plastic cranberry juice bottles with yellow, plastic twist lids on a shelf are visible behind Ennis' head. These bottles would have been glass until the early 1990's.
Jack is chopping wood when Aguirre approaches to give news of his sick uncle. Jack places the next log on the chopping block as he turns to speak to Aguirre. After the conversation is over and Jack turns back to chopping, the log is gone and he replaces the log that was never chopped.
During Jack's first and second bull rides, his free hand alternates several times from being his left or right hand. Since he's obviously not letting go to switch hands, either some shots are flipped or the sequence is edited from several takes.
Ennis, standing in the river washing a coffee pot with a rag, pauses to look up and spots Jack on horseback in the distance on a mountainside. Ennis then slings the washrag over his right shoulder and starts to exit the river. In the next scene, as he exits the river onto the riverbank, the washrag is gone from his shoulder and back to being held in his right hand.
When Jack rides into camp complaining that he is "commutin' four hours a day" he takes off one glove, the one on his left hand, to feel the coffee pot. It then shows him drinking coffee with his left hand and the right hand glove is still on and he is holding the glove from the left hand with his right hand. When Ennis says (the second time) "I wouldn't mind being out there" it shows Jack with the coffee cup still in his left hand but the glove from his right hand is now off.
At the beginning of the movie where we first see Jack Twist driving up in his truck, the window on the passenger side is up as evidenced by the reflections off the glass. Then as the truck turns into the parking lot, the same window is now down.
Towards the end of the movie when Alma Jr. visits her dad in his trailer, he goes to the cupboard to get them a drink and cups. The cupboard door at Ennis' head is seen alternately opened and closed without him touching it.
In the scene where Jack Twist is first introduced to Alma by Ennis, her purse is on her left shoulder and her arms are down - immediately in the next scene when she is shown, her arms are folded across her chest in a "defensive" stance.
Enis is helping Jack start his truck after they get back from Brokeback Mt.
As soon as the truck starts Enis slams the hood down, but it is not all the way closed. Enis then leans on the truck and he and Jack have a conversation.
In the next scene you see Jack driving the truck away and the hood is completely closed.
When Ennis receives Jack's first postcard it's sent general delivery because Jack didn't know Ennis's address. When Ennis writes back all he says is, "You bet," and leaves no return address, thus Jack still doesn't know where he lives (just the town). In the next scene Jack arrives at Ennis's apartment without this vital information.
During the rather important kitchen sink conversations after the family holiday dinner, a props tag is plainly visible on a dish's underside. As the dish is conspicuously hand-washed under running water, the underside faces the camera and the large masking tape tag with marker lettering goes unacknowledged by the cast.
When Ennis comes back to camp late at night after he encounters the bear, Jack asks him where he's been. It's supposed to be cold but when Jack talks you can't see his breath. When Ennis tells his story about the bear, you can see his breath, but when they continue talking, neither one's breath can be seen in the cold night air.