If Neville set his own trap, why put a pale faced dummy there? How does that lure a vamp?
Again metaphorical, he is going crazy. Why would we see the dummy move its head and later be at the end of the street? His mind was playing tricks on him yes, so it's not hard to say that from his perspective, the dummy was never real. you said it yourself, he didn't know the intelligence of the infected, maybe he figured they'd fall for it.
It was put there to confuse Neville and lure him to investigate. Next, Neville can only hunt during the day so the traps need to be shielded from the light. The snare had no sack to protect the vamps from the light like the other one did where he caught the female. Why would it be out in the open?
It was placed at the beginning of a hive entrance. It's not too far fetch to believe that would be a good place to place a killer snare. If i lived in a city full of monsters, why wouldn't I want to place one and pop off these guys a little bit at a time? Maybe the cloth didn't trigger correctly.
Neville can only snare the vamps during the day in front of a hive, it can't be out in the open. No vampire could come that far out during the day. If Neville can only hunt during the day, the vamp would have been dust by the time he collected it from the snare in daylight since the snare had no sack.
Again, maybe he just wanted to kill it..etc.. There doesn't have to be a reason.
The scene was set up to show us that Neville was wrong about their intelligence. The fact that the vamp had dogs on a LEASH and was clearly waiting for sundown to attack Neville was a dead giveaway.
Again, it was his insanity that led him to see the dummy there, that he saw earlier in the scene move its head. In desperation, he starts making lots of noise by shooting up all of the windows, therefore attracting the infected who are now watching him hang all day, waiting with dogs to kill him.
Just what more had to be made clear?