More Fun With Ice Spikes

Per this Caltech page on ice spikes, I tried freezing distilled water in an ice cube tray. I didn't get any of the impressive needles seen on this page, or anything like yesterday, but I did get a stubby little growth, seen here in the front right:

I also heard a rustling of ice a few minutes ago, and I think it was the cube seen above on the left, which had cracked and lifted out of its container. 

It has an interesting indentation on its top, about the size of your thumb from the base of your fingernail to the end of the thumb:

 

This ice cube tray is more rigid than the blue one I used yesterday (which still has its spiked cube); perhaps that makes a difference. I'll try distilled water in the blue one and see what happens.