When Ed lights the Molotov cocktail, it disappears when the zombies drag him.
When Shaun and Ed are throwing objects at Mary and the Fat Man in the garden, one of the first objects (and another later) goes through the back window and the interior curtains are seen to fly up in the air. When they run out of objects all of the windows are still intact.
The red mark from the leaky pen in Shaun's pocket changes size and shape several times even before he gets covered in Zombie blood.
When Shaun and Ed decide on the Winchester as a safe haven, it shows a closeup of the TV when the newscaster says not to save loved ones. Though out of focus, you can see the remote in Shaun's hand Then when Ed says, "Do you always believe what you hear on television," Shaun picks up the remote from the coffee table and turns off the TV.
When Shaun and Ed are in the back garden hitting the two zombies with a shovel and a cricket bat, their clothes get covered in blood, but the weapons remain immaculate. Later, in the living room, Ed holds up a blood covered shovel.
The Winchester rifle used in the film was stated to fire shells, something exclusive to shotguns not rifles.
When the shells start exploding one of the projectiles ricochets off of several items in the bar, however, this would be impossible since shells fire shrapnel which couldn't ricochet in that fashion.
When bullets are set off when exposed to heat and not in a firearm, it's the brass casing not the lead that flies off as its lighter.
When they're all in the car on the way to Liz' flat, Philip says "it's a 20 mile an hour zone". the movie is set in England, which uses kilometers per hour.
When Liz uses the fire extinguisher she is holding the horn with her left hand. This part of a CO2 extinguisher becomes very cold when fired - enough to burn skin. She should not have been able to do this without suffering injury.
When the 'Groom Zombie' enters Shaun, Ed and Pete's home you can see positioning markers on the floor in Shaun and Ed's reaction shot. Look to the lower right of the screen and you'll see at least two markers in blue tape on the floor. These are for continuity and should not be visible in the final cut.
In the opening montage, you see Mary the checkout girl, working at the supermarket. On her name-tag it says "Landis Supermarket", yet on the checkout it clearly reads "Asda Supermarket".
When Shaun runs out of Liz's Apartment to get to the car, when he hits every zombie with his cricket bat, it bends, revealing it's made of foam.
Behind Ed is another Zombie wearing jeans they only attacked the Zombie in a wedding suit.
Right as Ed smashes the one-armed zombie in the head with the ashtray, and for a few seconds afterward, the TV is visible in the background. Although the sound of the newscaster can still be heard, the TV flips a few times between showing the news, and a blank screen with AV3 shown at the top left with only the audio playing.
When Shaun first walks down stairs, he sits on the sofa and picks up a PlayStation controller we hear "Player 2 has entered the game" And "Player 2 has left the game" The game Ed is playing, TimeSplitters 2 (2002), does not have a press start to add players feature.
Each time Shaun opens the fridge door in the shop, the camera is reflected in the door.
When Liz jumps over the bar after Shaun, there is a bald man to the right trying to help Liz get over the bar.
When Shaun is climbing through Liz's window you can see the top part of a scaffolding pole from the platform he was standing on.
When Shaun and Ed reverse to check the zombie they've just run over, there is an UN-snipped cable tie attached to the fake demented leg of the zombie.
When they first start beating the pub owner with pool cues, the actor/stuntman is clearly wearing padding under the back of his shirt.
When Shaun is walking to the shop (for the second time - when the zombies are rampant), the boom is reflected in the blue car on the side of the street.
When Philip is bitten, everyone gets into the car. There is a quick reflection of it on the car.
Simon Pegg appears to shout 'Nick look out' as the car runs over the zombie, referring to actor Nick Frost and not his character, who is called Ed.
When Shaun and Ed are frisbeeing vinyl at their two zombierific backyard invaders, Shaun claims that a copy of New Order's "Blue Monday" is an original pressing. The first pressing of this 12" single in the UK was in a die-cut sleeve with a black insert, so the one in the film is obviously a later release.
In the pub attack scene, when Shaun moves away from the bar stool and Liz reclaims it, in the same shot there is a female zombie on the far left who is standing still with her arm resting on a booth, and staring right at the camera.
When Shaun is visiting the shop the first time, one of the newspapers can be seen to talk about a "Vacine," instead of "Vaccine."
In the pub when the zombies are breaking in, right after Liz yells "stay back", a few seconds later a subsequent shot shows her holding the bar stool up in the air instead of against the zombies.