Backlash is Tank #1 on Alpha. How long has Morpheus been in the program? When she was first around, it would've taken him a few encounters to really have it cemented in his head that she can't talk. Not in a deliberately offensive way, but more like -- he might've tried to start a conversation and then been like oh shit what do we do now when it's time for her to reply. He doesn't know ASL, but if she uses pads of paper/pencils to communicate he does know how to read! She just might have to tap the pad of paper to remind him to use his eyes instead of his ears sometimes.