Throughout a lengthy interview covering many different topics, a patient's expression remains fixed in an intense, suspicious wariness that never shifts, even when the conversation moves to neutral or pleasant subjects that would ordinarily change how someone looks. What is this?

This is stiffening of affect: an emotional state, once present, that becomes fixed and resistant to change even as circumstances shift in ways that would normally alter it, with the affect remaining full in intensity rather than reduced, exactly as described here with the intense, unshifting wariness. It is not blunting of affect, which concerns reduced range and intensity rather than a fixed intensity that simply will not shift. It is not incongruity of affect, which concerns a mismatch between the affect shown and the content or context, rather than a fixed emotional state that fails to move with changing topics. And it is not lability of affect, which is its near opposite: rapid, excessive shifting rather than rigid fixation.