Dr. Shinera, played by the great character actor, Maliachi Throne was a frequent Star Trek actor providing the voice of the "Keeper" in the first pilot, "The Cage", playing Commodore Jose Mendez in what became the the STOS two part episode "The Menagerie" that was created out of the pilot, and Senator Parde, in the STNT two part episode, "Unification".
Also interesting is a cool performance by a 32 year old rookie Tom Skerritt as Richardson, the First Officer of the ill fated submarine "Angler" in the teaser.
As Nelson and Crane come onto the island, we see a camera observing them. We see a second camera moments later. It is not facing Nelson and Crane; it's aimed to the left of the screen and the men are coming up from the right. The moment they pass the camera, it promptly swivels around and faces back the way they came.
The submarine Angler is nothing more than the Seaview model with a different nose and a decal with the ship's name on it. Likewise, the Angler's control room is a simple redress of the Seaview set.
The scene where Nelson, Crane, and General Tau appear to shift dramatically in size is a genuine optical illusion, not just a special effect.
Dr. Shinera: Darkness, absolute silence, complete isolation and the knowledge that you are surrounded by hostile forces that control your destiny, can frighten the bravest of men, General. But I don't want to frighten them, I only want to strip away a single layer of that veneer of civilization that covers the animal in each of us.
Nelson: Something about that island gives me goose flesh. It's like it's covered with slime.