Ice is a slippery terrain type found only in Area 3. If the Spelunker builds up any momentum while running on ice, he can easily slide off a platform or into an enemy. Spike shoes allow the Spelunker to retain his traction on ice. You can also stop yourself from sliding by ducking and/or crawling.
The Yeti King's roars are capable of turning harmless blocks of ice into icy pushable blocks. Because the "wet fur" level feeling, where the Yeti King appears, contains much more ice than the usual Area 3 level, this means that the Yeti King has lots of opportunities to crush the Spelunker under a block of ice shaken loose from the ceiling.