He barely notices the dead birds; makes a note of them and passes on. On the Island, such a sight would have horrified him. Here, it hardly seems worth comment. It's all context, maybe.

"You remember how to use it?" he asks, catching Neil's eyes in the mirror as they bump and jostle over potholes and splash through mud that paints the sides of the car and sends dirty flecks in through the wire grille. He's sure Neil does, but he's asking anyway, for his own peace of mind if for nothing else. And to remind Neil that here, he might truly have to know how to kill someone. No more playing, no more games.