Brennan wanted to respond with 'of course you didn't,' but didn't. It really wasn't necessary. He was a little high on the annoyed scale at the moment, but it wasn't enough for him to lash out at David, as easy as that could be. He had other things to think about, namely the swimmer David had seen, to be spending his time berating the guy. He'd been a little more on edge lately for plenty of reasons, and that lent him to be more verbal with his displeasure in some of the other survivors on the island. It really was almost like venting or projection or whatever the psychology term was (it had been years since he'd taken that class in school, and he'd be damned if he could actually remember any of that with as much clarity that he had for being able to distinguish types of infected, the best way to kill them and how the plan a strategy in a split second).
Instead of his initial response, Brennan settled with "alright," as he took another look at David. "That's understandable," he continued, strangely understanding considering how annoyed he was. Fear was fear, and no one left could claim they were fearless; Brennan certainly wouldn't. Fear was an evolutionary miracle, and as much as he hated the vulnerability that came with it sometimes, he couldn't help but appreciate the way it could motivate him too.
"They really only have a stronger upper body. It might not even be physically capable of jumping out of the water. Usually they just pull people in."
He wasn't going to wait for the creature to pick a spot on the pier to hide out for some unsuspecting person to head out that way. Brennan judged how deep the water was around the infected and decided to just head along the pier after it. The water was pretty calm despite the creature's spastic movements which Brennan quickly took care of, dispatching the infected before it even had a clue what was about to happen to it. Sometimes it almost seemed too easy when there was only a sole infected, but his job was done and he had other places to check.
"Be more careful when you're heading out on the pier," Brennan admonished, sounding like some sort of preaching teacher or something. That annoyed tone only served to make him even more annoyed and taking care of that infected (because thinking that he was 'killing' them forced him to remember that it had been someone's spouse or parent or child and he didn't really want the guilt of acknowledging that) hadn't really helped all that much. "The currents aren't as strong today and it might be more likely for them to reach the docks."