One of the most common tropes of horror movies is that all of the characters often make very stupid decisions, not using common sense and intelligence to avoid being killed. Shaun of the Dead is no different in that regard, although it is set in a real-world situation with characters who react and respond as people would, there is still a varying degree of intelligence throughout the film.
Some of the characters refuse to use their brains in order to make basic decisions, while others are able to take control and showcase great intelligence in a bid to try and survive the zombie apocalypse.
Cousin Tom
Cousin Tom is barely shown within the movie, but Matt Lucas' brief appearance being part of the opposite group that Shaun and his friends bump into on their journey. Each member of the opposite group is supposed to be the clear opposite of members of Shaun's group.
Cousin Tom is supposed to be the 'Ed' of their group, and considering he's one of the least intelligent people in the film, there's no doubt that Cousin Tom also falls into that category, spending his time focusing on his phone rather than anything else.
Ed
He might be the most likeable and funny character within Shaun of the Dead, but sadly, Ed is not the smartest. He doesn't make simple decisions and seems to struggle understanding certain things, however, he is happy enough to fight against the zombies, which makes him very useful.
Of course, by the end of the movie, Ed is also a zombie, which lowers his intelligence even more, although he's still capable of playing on the PlayStation.
David
David is one of those people who likes to think he's incredibly smart, but that isn't actually the case. He's someone who tends to say a lot and wants to question absolutely everything, but he isn't always the man to lead by example or put things into action.
David analyzes every scenario, to the point of moaning and groaning about everything that happens throughout the movie. However, that ultimately is his downfall, and the fact that everyone else finds him incredibly annoying is a clear sign as to him not actually helping.
Barbara
Shaun's mom is a fantastic character and she brings a lot of humor and serious emotion to the movie throughout her involvement. However, when it comes to intelligence, Barbara isn't one of the brightest characters in the movie, mainly because she's a little bit ditzy.
Barbara doesn't seem to be aware of the clear issue that is taking shape in the form of a zombie apocalypse, instead, being more puzzled about everything that is going on around her. She might be incredibly sweet and kind, but she's just not the smartest.
Pete
Pete is only a supporting character in the film, being involved early on as he shares a flat with Shaun. While they're clearly good friends, there is a little bit of tension between them, mainly because Pete doesn't think that Shaun is taking his life seriously enough.
He, on the other hand, has a good job and is clearly an intelligent person. Although he doesn't last long in the movie due to the zombie apocalypse, he is one of the smartest characters who appear throughout the film.
Philip
Bill Nighy plays the character of Philip really well throughout the movie, being someone who is quite grumpy and closed off at the start, as his relationship with Shaun is clearly difficult. However, Philip does show that he's a smart person by the way he reacts to the situation.
Even once he's been bitten, Philip still manages to think for himself and puts together some incredibly emotional moments with Shaun, explaining his decisions and his ability to that, even in clear pain shows the intelligence that he has.
Yvonne
It's hard to rank Yvonne too highly because she's not in the movie enough to really justify what her true intelligence is. However, when the two groups share an awkwardly funny meeting in the middle of the apocalypse, she is clearly shown to be the leader of her group.
Being in that position showcases strength and intelligence. Much like Shaun, she takes control of her group's situation and ensures that they will be able to survive, creating a plan of action even in difficult circumstances.
Dianne
Dianne is one of the best characters in this horror movie, mainly because she has absolutely no filter. She sees through absolutely everyone and is a great judge of character, having no problem in saying it how it is, which is a real sign of intelligence.
Dianne also responds well to the difficult situation that the group is in, showcasing real intelligence and an ability to overcome any problem. She thinks outside of the box and is happy to get stuck in, despite any fears that she may have.
Liz
The girl of Shaun's dreams and the one who is happy to question things, using more common sense than pretty much every other character within this film. There's no doubt that Liz is an intelligent woman, and she is happy to showcase that throughout the journey.
She makes good decisions and thinks on her feet very well. Liz is able to help Shaun due to their closeness and that allows her to be a leader as well, as she helps keep Shaun going, despite his difficult emotions at points.
Shaun
Shaun isn't particularly intelligent to the point where he would be considered clever. However, within the confinements of this movie, he is certainly the smartest character of the bunch. His plan to have a beer and let things blow over is ridiculous, but he's the only one willing to take control and make a plan to begin with.
He manages to successfully navigate all manner of situations, and even though he loses loved ones along the way, Shaun still manages to act incredibly smartly. He responds perfectly to high-pressure situations and it is through that he really showcases his brains.