Thane turns around and walks back toward the other room with no indication that he heard April. For the time being she's inconsequential. Unworthy of attention, unworthy of response. Let her whistle in the darkness.

He'll wait a couple hours to see if Sato does sleep. If she does, he'll see if it hits REM. If not, no bonus, no foul. The work of systematically dismantling the Doctor's life begins.