He couldn’t understand why these things were basically white—which didn’t seem very stealthy—until he got close. Then he saw that the whole thing was jacketed in a thick layer of frost. Humidity had condensed out of Tuaba’s air and frozen on contact. It must have been dropped from the stratosphere—from an airplane flying so high it couldn’t be seen. It had fallen for miles through air at nearly cryogenic temperatures and become ice cold. That explained the oxygen masks that these guys all wore.