At about 43:45, when Kate comes up behind the vampire that is attacking Jacob, the chainsaw has no chain on the bar. You can see the sprocket on the end of the bar and there is no chain, but when Kate cuts through the vampire there is a chain on the bar.
It had been stated that, like vampire lore, they can be killed by a stake through the heart. When Seth kills the doorman, as he falls you can clearly see the stake sticking in his stomach, no where near the heart.