What makes ice shatter in icecube tray? I have two identical ice cube trays. When I twist the trays to remove ice, sometimes the whole cubes pop out perfectly, but sometimes they shatter and I get lots of shards with bits of ice stuck to the bottoms of the molds.

What can I do to consistently get the whole cubes out?
what i used to do for popping whole cubes is-take out the ice tray from freezer. Put it under running tap of normal temp water(for 2-4 secs) from both sides of ice tray,from top and bottom back of ice tray. then twist the trays to remove ice. It pops out shattered ice less frequently.