Paranoid
Lost track of how many times I've seen the film, and I've read the novel twice.
My take is that HAL folds under the dual stress of responsibility and imposed deception, and goes quietly, madly paranoid.
He's already made up his mind that the crew (not just Bowman and Poole) are a threat to the mission.
Like a madman, he conjurs up the AE-35 failure as a sort of test (Of Bowman & Poole) that can only fail.
So,...when Bowman tells HAL to rotate the Pod, in an attemp to see if HAL can read lips, HAL intentionally decieves him and pretends he cannot,...in order to evesdrop on their conversation.