Ice
Ice, ., is formed when a pool is frozen by a spell or wand of cold. It is slippery, and when you are walking on it, you will fumble, just like when wearing gauntlets of fumbling or fumble boots.
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.'