When the gang is hiding from the walkers under the cars, T-dog gets spotted by one of the walkers. He cuts his arm on a car door and blood starts spraying out. When he gets up to run in the other direction, his arm is normal.
The amount of dirt, and hair growth, on Shane's face changes continually. At the start of the argument with Lori, there is no evidence of dirt on his top lip. From the next camera angle, his face is filthy. This changes during the argument. When he next speaks, to Andrea, his face is clean and his hair growth substantially less. Afterwards, back in the woods, his face is dirty again.
At approximately 32:36, when Dale is pointing his rifle towards Shane, a mark on Shane's T-shirt from a previous take can already be seen, before Shane actually steps forward to Dale and presses his torso against the barrel, hence the mark.
From approximately 0:57-0:59, as Daryl approaches the tent, he is holding his crossbow and draws his knife. In the next shot he is only holding the knife. As he exits the tent he still has only the knife but in the next shot he is slinging his crossbow over his shoulder. During the shots where Daryl is not holding his crossbow, it is nowhere to be seen - he didn't drop it on the ground, nor did he hand it off to Shane or Rick.
The sweat stains on T-Dog's shirt change between shots while he is talking to Dale.
There is a crucifix with Christ on the cross in a Southern Baptist Church. The Southern Baptist denomination doesn't use that as a symbol.
The Glock that appears to belong to Shane has an obvious 10-round reduced capacity magazine, common during the 1994-2004 assault weapon ban and still used in states where such magazine restrictions currently exist. Full capacity magazines (15 or 17 rounds depending on the Glock pistol model) have always been in use by law enforcement; additionally, these would be legally available to civilians after 2004 (assuming TWD takes place in current times) in most states, including Georgia.
+A lot of people point out that the Hyundai SUV that Shane finds is a 2011 model, and therefore couldn't be there since the outbreak happened in 2010. However cars are manufactured, and often sold, in the year leading up to their "model year". So the Hyundai Shane finds could be one someone had just purchased, and even if that model wasn't on the market yet, it is possible someone could of taken it from an assembly plant lot.
The electronic bell at the church could be hooked up to a battery. We have seen things like radios hooked up to car batteries in other episodes, so it is quite possible someone at the church hooked the PA system up to a car battery.
During the opening credits the freeway leading out of Atlanta is shown with a log jam of cars and a bus. The opposite direction lanes are separated by a median about as wide as the 5 lanes on the freeway. During episode 7, season 1 (What Lies Ahead) the same shot of the backed up cars & one bus is used in a different section of the freeway--much closer to downtown Atlanta and the opposite direction lanes are immediately next to the blocked side. This shot is also used in an earlier episode, too.
At 23:41 Rick prepares to bash a walker in the head with a rock. He squeezes the rock with his left index finger, revealing it to be made of foam or rubber.
When Carol is praying in the Church, Rick's shadow is higher on the wall than his height, indicating a low-level light illuminating him. Then, when Carol moves to sit down, she casts two shadows on the wall. The rails around the image of Jesus also create shadows which are not consistent with the angle of the sun when they enter the church.
At 12:20 Dale is on the RV's roof spotting with binoculars. From 13:05 to 13:22 dozens of walkers have popped up out of nowhere.
The group members are constantly reminding themselves to avoid loud noise lest they call walkers to the area yet Darryl is constantly gunning the engine on his motorcycle.
From 0:10:08 to 0:10:13, right after Daryl pops the gas door for T-Dog, the crossbow bolt that Daryl is holding in his mouth is missing the point; the threads where the points are screwed in are clearly visible.
The scene when Andrea is trapped inside Dale's Winnebago and is forced to kill the walker with a screw driver. Just after the walker drops to the floor after being stabbed several times in the eye, the camera looks up from a low angle at Andrea. The blood from the walker on her face runs into her right eye. This should cause Andrea to become infected as every scene involving walker blood they're told to not get it in their eyes or mouth.
Though society has supposedly collapsed, and all services have broken down, the church still has electricity to run its automated church bell speaker and sound system.
It is mentioned at the CDC in Season 1 that the power grid is down, yet the speaker for the clock ringing at the baptist church is working, running on a timer.