All of the graphics (for example, the explanation of the Babel Fish) were drawn by hand and animated by rostrum camera. They were not produced on a computer.
Life. Don't talk to me about life.
The person operating Zaphod's third arm can be seen on multiple occasions.
After the credits for episode 3, the voice of the book returns briefly to resolve which one of the characters sustained a bruised arm -- a question that had been raised earlier in the episode, but left unanswered because it was unimportant.
For the original run in the United States, the six-part series was edited into seven parts (since the original episodes all ran over thirty minutes and could not fit into the rigid 30-minute time slot). An interesting sidenote to this is that when the six 35-minute episodes were made into seven 30-minute episodes, the plot recap intended for the beginning of each episode appeared five minutes later in the program with each subsequent installment (and did not appear at all in the final episode!) After this version was televised on PBS stations a few times, the program disappeared from American airwaves for a while. Then the original version, with its six slightly overlong episodes, showed up, and that's all that's been seen on public TV since.