system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are some patches of ice more slippery than other patches?
gpt
Ice is slippery when there is nothing on it to provide friction.

So if you spread sand over it, even is small amounts, it will already be less slippery.

When there is damage to the surface, even the smallest ribbles caused by melting and freezing again, that will make it already less slippery.