Mello does happen to glance back at Near - sensing, perhaps, a slight shift in Near's typical unruffled demeanor, or maybe simply because he's been too quiet for too long, and Mello is feeling extra paranoid in this fog. Whatever the reason, he sees the creature approaching, and alarm bells go off in his head.

"Near." There's a note of urgency in his tone; surely he's seen it too, but Mello isn't going to take chances.