Title text:
The speed of light in air is 50% faster than in fiber, but it's a challenge to get the arms to move fast enough to realize the latency advantage.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3295/
Didn't get the semaphore part and thought those were fans with a wind speed sensor below, glad there's explainxkcd lol.
Using fans would make for a far worse connection than the one on the comic, at least that one is easily full duplex and somewhat free of interference.