Kirk says that the pirate can't be killed after he's brought through the tunnel. If that's true, then Tony and Doug should be invulnerable outside of their time as well, which clearly isn't the case.
This episode may be the first when it is really noticeable, but several times in the series when the guys "land" they are obviously hanging from moving cables and letting go to create the effect of momentum. In previous episodes it looked as if they were just being thrown, but the shadows of the cables are clearly visible here.
Probably not the first time this has happened, but as Berkhart walks into the tunnel, you can see his shadow on the "infinite" matte shot directly in front of him.
Mr. Johnson: (talking about time travel) Gentleman. I pride myself on being a man of logic. I'll have to think about that one.
Captain Beal: You must have money.
Tony: I have some relatives in Philadelphia. Problem is, they haven't been born yet.
This was the tenth "Time Tunnel" episode to be filmed but was Episode 23 in the transmission order. Over the course of the filming of the show, James Darren's hairstyle changed subtly but noticeably - look closely and you'll see that in this episode, his hair once again has the slick, glossy look of the early episodes.
This is the last episode that has the "Two American Scientists ..." voiceover at the beginning. All subsequent episodes begin with the Time Tunnel staff watching Tony and Doug on the tunnel's "image area" as they tumble helplessly through the time vortex - with no commentary.