Ice
Ice, ., is formed when a pool is frozen by a spell, wand of cold, frost horn. It is slippery, and when you are walking on it, you may fumble, just like when wearing gauntlets of fumbling or fumble boots. Wearing boots with the description 'snow boots' makes ice behave just like normal terrain (unless snow boots are fumble boots, in which case you will continue to suffer from the effects, but for a different reason).
Beware fire-breathing monsters, wands of fire, fire traps and such effects if you are on ice; those will melt it.
Corpses rot slower if they're on ice.
Items on ice will slide further when kicked, upon kicking them you get the message 'Whee! a\an\the item slides across the ice.'
Message generated from pools (not moats) being frozen into ice is "The water freezes" ("The water freezes for a moment" when attempting to freeze water on the Plane of Water.)
