curling update...i still don't understand this sport

See the pictured curling stone, or "rock," in the parlance of our times.

Curling can best be described to the layman as shuffleboard on ice. But no person outside the curling community will ever understand the sport. This evening, the commentator made the most confusing remark I've ever heard...

"Wow. The skill level in curling has really advanced! These guys are just able to hit the corners of those rocks so much better than they could just a few years ago!"

To me, that rock does not appear to have "corners." Am I missing something obvious?