Basic physics?

Got up, shivered, looked out, thought...."Who the hell stuck that shard of ice up there?"
The Lurgi of the last couple of days has faded to "severe nuisance" status i.e. I've decided to live. Last night I couldn't keep warm, maybe the 110˚F had something to do with that. Today I can breathe through my nose again and walk around in "shirtsleeve order" again.

When I got out and studied the shard, I found
A) It was an integral part of the freeze.
B) It was hollow for most of its height and I was able to pour out the tiny quantity of water in the "horn".
C) There was plenty, unfrozen, water beneath.

I know how it happened. I'll raise a small cheer for any correct answers.