The blood spatters on Willow's shirt change thickness and pattern throughout.
When Buffy is on the operating table, you can hear the beep of the heart monitor as well as the flat-line. But on closer view, you can see that she is not connected to the monitor.
Even after a day after the shooting, the blood on Buffy and Xander's shirts is still bright red and kind of moist. After that much time, it would've been much darker, dry and caked up.
Buffy mentions a couple of times that, "We don't kill humans." But, in season five's Spiral (2001) is when the Knights of Byzantium attack Buffy and friends on the bus, and she kills a number of them. They were humans.
When Willow is walking through the forest tracking Warren, ropes can be seen pulling the trees back as she walks by.
In the shots of vines ensnaring Warren's legs, you can see a leaf-strewn tarp shifting around underfoot in place of an actual forest floor.
Around 15m, Willow extracts the bullet from Buffy's wound by means of magic. The bullet was in pristine condition, which cannot be possible, even if it were a full-metal jacket.