The tube must have been made of glass, otherwise it could not keep the air out of the low-pressure interior.

However, you are right that a minimal precaution would be to wrap the tube in a transparent plastic film, preferably glued to the glass, in order to contain any broken shards.

It may not have been a neon tube, it may have been a plexiglass tube with LED lights and a diffuser. How can you tell from inside an esophagus?

pretty sure half the trick is a before-and-after experience

actually pissing my pants at the thought of some guy walking onto the stage, revealing his glowing torso, then walking off again

I recall it looking bright like a neon tube with the glow that neon tubes emit -- also with heavy duty cable going into the neon tube. He swallows the sword on stage so everyone sees the sword go in and out.

I also had no doubt to believe it wasn't a glass neon tube.

Sorry, I meant in the hypothetical case where someone swallows a "neon" tube without any shielding. The metal cage in your case tells me that it was probably legitimate.

Though, what happened to the other end of the wire?

It was plugged into the wall through I'm guessing a high voltage neon transformer.

I have no idea if the cage was grounded or not. I assume it wasn't, which should have been fine if the connection to the tube was outside of his mouth.

There’s a thing Penn and Teller talk about (in the nail gun routine) about how it is immoral for a trick to have any real danger as it makes the audience complicit in risk. This resonates with me considerably.

But then you move further from magic and closer to acrobatics and things like tightrope acts without nets have real danger.

Juggling, circus acts, and heck even air shows can be dangerous for the performers. I've seen an air show performer die during his act a few years ago when he crashed into the ground.

Even the NFL has a good amount of danger during every game -- and people get injured.

But spectators have died during Airshows [0] and during, say, the Indy 500 [1].

[0]: https://www.history.com/this-day-in-history/air-show-acciden...

[1]: https://www.sportscasting.com/indianapolis-500-tragedy-rarel...

Airshows have also killed people not spectating, but just driving nearby when the plane crashed into a main road: https://en.wikipedia.org/wiki/2015_Shoreham_Airshow_crash

When I saw Penn & Teller live in the same show they did the routine you describe, but also a fire eating routine about how some stunts simply do hurt, and can be dangerous to both learn and perform. Neither break the "no permanent damage" rule but you are left with two seemingly contradictory arguments.

Properly aligned you can fit the two ideas together, but I think they kind of personal mental arranging of ideas is exactly what they want to leave you with.