Last night at dinner I ordered a 6 once steak, cooked medium. They brought it back to me, red/raw on the inside. The took it away, brought me another steak, I cut into it like the mid center section of the steak, as I cut it, there was a HOLE inside the steak and it was black inside the hole, what the heck was that???
In a busy restaurant, steak is generally cooked by feel. Since you returned this steak as under cooked for your preference, the cook probably measured the temperature with a probe thermometer. The hole was probably a puncture, where the cook inserted a probe thermometer to ensure your returned steak was cooked accurately.