 Browning, Ricou (qv), a professional diver and swimmer, was  required to hold his breath for up to 4 minutes at a time for his  underwater role as the "Gill Man." The directors logic was that the  air would have to travel through the monsters gills and thus not  reveal air bubbles from his mouth or nose. Thus, the costume was  designed without an air tank. In the subsequent films, this detail  was ignored and air can be seen emanating from the top of the  creatures head.