The following contains spoilers for WandaVision episode 8.
The newest episode of WandaVision was full of revelations, mostly about Wanda Maximoff's past and the trauma she has endured throughout her life. One of the notable moments in the episode revolves around Wanda and her family in Sokovia when she was a child, gathered around the TV watching old American sitcoms. These shows were a way for her family to bond, as well as learn English. Sitcoms have clearly become a coping mechanism for Wanda, because the problems in those shows are always easily solved by the end of the half-hour, and everyone is happy once again (hence why her Westview reality took the form of various sitcoms).
The specific show they're watching in this scene is The Dick Van Dyke show, a sitcom from the 1960s starring Dick Van Dyke and Mary Tyler Moore. The exact episode that they're watching is season 2, episode 20, and is called "It May Look Like A Walnut." Though the overall idea of Wanda being attached to sitcoms is important, this specific episode they're watching actually has significance in the context of WandaVision.
"It May Look Like A Walnut" begins with Rob (Dick Van Dyke) and his wife Laura (Mary Tyler Moore) watching a sci-fi movie in their twin beds. The movie is about an alien from the planet Twilo named Kolok, who is using small devices that look like walnuts to hit Earthlings with a chemical ray that will turn them into Twiloites, with no thumbs and an extra set of eyes. Laura is scared by the film, and Rob teases her by making noises and trying to scare her even more. The next morning, Rob wakes up and sees walnuts all over the house. At first he thinks that Laura is just getting back at him for scaring her the previous night, but she denies it.
The walnuts even begin showing up at Rob's workplace. His coworkers are also acting strangely, and claim that Kolok is a real person. Rob also starts to believe that the characters and events from the sci-fi film are happening, and that Twilo and Kolok are real. He runs home to find Laura, and when he does, he finds a closet full of walnuts, with Laura in amongst the cascade. She claims she is from Twilo and wants to turn Rob into a Twiloite. Rob then wakes up, back in his bedroom, and discovers that the whole day has been a dream, and that Laura has been having nightmares as well.
This episode was obviously chosen very intentionally by Marvel. First of all, the beginning of "It May Look Like A Walnut" mirrors WandaVision episode 2, where Wanda and Vision are sleeping in two separate twin beds (similar to Rob and Laura's setup) and are scared of something. In Wanda and Vision's case, it's noises coming from outside rather than a sci-fi movie, but the similarities are still there.
More importantly, a majority of "It May Look Like A Walnut" takes place inside of a dream-like reality, where the main character is unaware that what he's experiencing isn't real. This is similar to Vision's journey throughout WandaVision, where at first he believes everything to be normal, then begins to clue into the feeling that something about his reality is wrong. Just as Rob questions his wife and co-workers about the sudden and mysterious appearance of the walnuts, Vision questions the people around him when he senses something is off. In both cases, everyone at first insists that everything is normal, with the truth slowly unravelling that something is amiss as the show goes on.
In "It May Look Like a Walnut", the final conflict ends up being that Rob's own wife is trying to use alien powers on him and to turn him into something he's not. This is a little more sinister than Wanda's intentions with Vision, but the conceit is still the same - Vision discovers that Wanda is the one controlling everything and actually has ulterior motives behind this seemingly-picture-perfect life. He learns that he is supposed to be dead, but she has brought him back (although we now know that she has actually fully recreated him out of nothing), in a way making him into something he's really not.
The goal of Korok and the Twiloites is to change humans to fit their will. Again, while this is more obviously sinister, it is similar to what Wanda did to the citizens of Westview, controlling them to fit her narrative of the happy little sitcom town. This episode of The Dick Van Dyke show is all about a dream world, where reality has shifted and there is something dark going on. This is the tone that WandaVision has always taken, especially in the first half of the season before viewers really started getting answers. It's a very fitting episode to choose as something that has influenced Wanda, as it was one of the last happy memories she had with her family before everything got taken from her.
It remains to be seen whether "It May Look Like A Walnut" will have any further significance to WandaVision's final episode, or whether is was just a clever, one-off way to reference what WandaVision has been about so far. Clearly, Wanda's control over Westview is directly influenced by these sitcoms, but since that reality is coming crashing down around her, viewers now get to wonder whether or not WandaVision will get that happy, Dick Van Dyke Show ending.