In all honesty, he has forgotten that he only needs to kill one of them. He still has four rounds left in the magazine. It would be harder for him not to pull the bolt back, chamber the next round, and catch the easy target as it wings around to glide back in on an easily-predictable trajectory.

When he pulls the trigger and drops the second target, it's clear that he is faring much better with these living, thinking targets than he had with the inanimate ones from earlier, even with it being the middle of the night.

It isn't until he chambers the third round that he actually takes a moment to think and assess, scanning the field for any remaining targets and estimating his likelihood of being able to take down another.