That would be a “zwarte mees” or “black tit”. I guess that’s a fitting name as well

You’re right! My mistake here was in translation, as the Dutch name is “koolmees”, which literally translates to “coal tit”. I’ve edited the post title

That’s what prompted me to post! I had just taken these pictures when I saw your post

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The general idea is correct, but since we’re dealing with electronagnetic waves, they travel slower in any medium. So pumping out all the air of the room would technically make your wifi faster.

Liquid oxygen has (I think) a refractive index of about 1.2, so it would make the signals 20% slower (still very fast)