I don’t know whether this has been discussed, but here’s my take on the symbolism of knives in the film. If others have discussed this, maybe my post will add something new.
I believe there are no throw-away lines or scenes in BBM. Everything is there for a reason.
I also believe that in every line there is text, subtext, and metaphor/symbolism. So here’s my take on knives.
There are several significant occurrences of knives in the film. The first is when Ennis is lying in the tent carving a little horsey. We already know that horses symbolism Ennis. So, he is carving himself. This has been a major plotline throughout the entire film – Ennis always trying to create a happier, whole Ennis. Throughout the film, he fails miserably, his carving is never completed. But at the end, starting with his breakdown at the final lake scene, and continuing with the revelations he gets from Cassie, Lureen, Mr. and Mrs. Twist, and the shirts, he starts to make progress. In Jack’s bedroom, the first thing Ennis does is he picks up a little horse and cowboy statuette. We know this couldn’t be the one that Ennis was working on because it’s much smaller, more frail, and it has a rider on it. This toy is evocative of Jack and his cowboy dreams, but it also is a visual clue to us that Ennis is finally on his road to finishing the carving he started back on Brokeback Mountain. Also, that Jack’s carving (forming of himself) was more complete much earlier on than was Ennis’.
The next significant knife is the one Jack uses to peel his potato while Ennis peels his clothes off. Jack is peeling himself. Yes, Jack is a potato. Jack is beginning to peel away his outer layer of his homosexuality. Up until now, he has been interested in Ennis, stealing glances here and there, but he has not really started to “make his move,” if you will. He has worked his can opener on Ennis, and will continue to do so, but it’s after this scene that Jack starts his “not-just-friendship” actions with Ennis. This is further reinforced by the Basque. The Basque is a very important character in the early part of the film. He’s there to clue Ennis in on timing. The only time restriction that Ennis has on the mountain is to meet the Basque every Friday at noon. The one time we see Ennis meet the Basque for deliveries, the Basque tells Ennis that it’s too early in the summer for soup (to be sick of beans) – he’s telling Ennis that it’s too early in Ennis’ development to start a relationship with Jack – Ennis tried to order soup – a sexual relationship with Jack -- but was stuck with beans – a friendship relationship with Jack – but it’s too early for him. Likewise, when Ennis asks why he didn’t get the spuds in this delivery, he’s told that there are none. There isn’t a potato yet for Jack to peel – metaphorically, Jack is not yet ready either. It’s immediately after the Basque scene that Ennis is confronted by the bear and is thrown from his horse, who was spooked. Ennis was confronted by his fears and was spooked and he, himself, was thrown. Immediately after Jack peels his potato (he’s getting ready to go further with Ennis) is the ‘yee-haw’ scene where Jack sees his opening – the sad pall brought down on their conversation by Ennis telling Jack that “Hell, that’s the most I’ve spoke in a year.” And Jack takes his opening, and does his little mating dance for Ennis – Yee-Haw!
They use their knives to carve or form themselves.
The next significant appearance of a knife is when Alma suggests that she and Ennis and Jack go to the Knife and Fork together. Ennis shoots down this idea. Metaphorically, Ennis will not let another person carve up their relationship which he knows he is just about to reignite. Ennis says that Jack isn’t the restaurant type – he’s not the type to let someone else take control and carve – and that they’ll just go out and get drunk – whenever Jack drinks alcohol, he takes control of something, whenever Ennis drinks alcohol he loses control of something – often, himself.
The next significant occurrence is at the Thanksgiving dinners. Here, two old birds get carved. The two old birds were, according to Ennis, Earl and Rich. But Ennis and Jack are also two old birds. When Ennis tells Jack the Earl death story, Ennis himself is comparing Earl’s and Rich’s situation to Jack’s and Ennis’, making Jack and Ennis a pair of old birds. At Thanksgiving at the Twist home, LD Newsome starts to carve up the old bird, Jack. But Jack will not have it. Jack takes control of his home and his family and metaphorically says “If anyone is going to carve this bird (me), then it’s going to be me.” And Jack picks up the knife and carves.
At Alma’s Thanksgiving Spectacular, the old bird is being carved by Monroe. Here, Ennis is not in control of his life or family. Someone new has come into the picture, replacing Ennis in his roles of husband and father. He cannot wrest this away from Monroe, and Monroe continues carving their old bird, Ennis. (Aside -- Now Monroe uses an electric knife and Jack uses a fancy-dancy carving set. There may be some symbolism in here, but I’ll bet the only real significance of the electric knife is that it was Ennis’ wedding gift to Alma and Monroe.
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The final significant appearance of knives is in Ennis’ trailer in the final scene. He has not one, but two sets of knives in knife blocks. Because of the revelations he has had concerning the true meaning of his relationship with Jack (the final lake scene breakdown, Cassie, Lureen, the Twists, and the shirts), Ennis is now ready to really take control of carving his life into something that will make him happier and whole. There are so many knives there either because he’s going to get really good at it, or because it’ll still take him a long time. He was good back on Brokeback at tying things in knots, and he continued this throughout the film by tying himself in knots with his disassociations between what he felt for Jack and what he was taught to be the truth of such a thing. Now he has all the knives he needs to cut those knots free.
Now, what have we learned boys and girls?
That knives symbolize the men carving or forming themselves, that each man is responsible for doing his own carving or forming, and most importantly, that Jack is a potato.