He could make a rational inference about what these abilities are. If Jean is fire, and therefore Summer, his abilities leaning towards cold and ice makes him think of Winter.

He thinks, first, of snow-laden peaks filled with cold cadets training. Then he thinks further back, to bitterly cold winters with his father; listening to his coughing get worse and worse and doing what he could to secure anything warm.

There's very little reflected on his face, just a somber expression. He lifts a hand, instead, feeling ice form along his palm.

"Do we know for sure we have bodies to return to?" he asks, meeting Jean's gaze after a moment. The implication is clear; Bertholdt knows that he should not be here, that all that is left is a headless corpse.