That, and proving bias, Member.
The fact that it's on record that he called Oscar to discuss it again because Oscar's version to him didn't initially make sense. Then insisting that there were certainly the startle noises which is what the whole of his expert testimony was based on. Initially he said that he wasn't there to state aspects as fact, and that his testimony would be the same science regardless of the facts... but then getting caught up about him not being able to discuss whether one startle situation would be enough, because he 'knows' that there were two further startles.
In fact, all he actually 'knows' is that Pistorius said there were three startle noises. To my mind he should have been able to say what the science would have been if there had only been one startle. Even if he'd had just said 'logically, there will have been a build up if there were two, three or four startles'. But he didn't; he said he couldn't speculate because he knew there were two more startles.
In short, he will not entertain the possibility that Pistorius might be lying. His version, as far as the witness is concerned, is the true event, and he can't apply his science to any other version.