Kiyotaka, or rather Kiyondo as he claims to be after something happened, and Makoto were in the Physic lab, and Monokuma was explaining that the huge machine in the center of the room is an air purifier and that it's here because the air is toxic and if it wasn't purified everyone'd die. Then, Monokuma left before Makoto can question his words.

Kiyotaka: Come on, it's obviously a lie, Naegi! The air being toxic? Who would be stupid enough to believe that?!