User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-3150696-20110716081949/@comment-1758220-20110717012027

I think the frost sac could function by allowing Blangonga's (fully-developed) respiratory system to collect moisture out of the air it breathes which is absorbed into the frost sac. Inside the sac, the moisture mixes with a fluid that freezes upon contact with air. When needed, Blangonga takes a deep breath, and instead of breathing out of its lungs, it exhales through the frost sac, sending the fluid spraying forward and instantly freezing into a cloud of ice.

Steel Uragaans chin stub is likely red because it is constantly half-molten. The minerals that gather on the chin to form the stub are likely more malleable and have a lower melting point that that of the regular Uragaan, thus, the chin is hot enough to get red-hod, but not quite hot enough to begin liquidizing.

As for fire underwater, I may just have to blame it on it not being fair if Capcom were to disallow any fire effect underwater, rendering any fire-type weapon useless, against monsters like Lagiacrus no less.