Which episode in the original Star Trek series featured a verbal countdown (Scotty and Spock I think)? I remember the camera focusing on their mouths part of the time.
"Let That Be Your Last Battlefield"
The human crewmembers don't actually say the countdown timer, but the camera notably focuses quite tightly on Kirk, Spock, and Scotty as they give their authorization codes for the Enterprise's self-destruct sequence. The scene is on YouTube: