When Glenn arrives at the camp, he gets out of the car and shuts the door. Shane tells him to pop the hood and the door is wide open again, without there being any time for Glenn to react and open it.
When Rick and Lori are laying on a cot together in their tent the background sound effect of insects chirping cuts in and out a few times.
The person standing by the Dodge Challenger when Rick is hugging Lori and Carl after reuniting with them is not a crew member, it is actor Steven Yeun (Glenn).
As Glenn is speeding toward the camp in the stolen car and he rounds the curve on the dirt path, the tires squeal like they're on a paved road. They wouldn't make this sound on dirt.
Once Merle gets the hacksaw he could cut the bolt to which the handcuff is locked. This would take only a couple of minutes, or he could cut the chain holding the cuffs together. This would not be as easy but still possible. Instead he chooses to cut his hand off. This would take quite a bit longer than the chain, would be incredibly painful, risk death from blood loss or infection and would permanently disable him in a world where having both hand could be the difference between surviving or not. Merle is stupid, but he isn't THAT stupid.