The first time Demeter warns about Macavity, it seems like a false alarm, as it's only Mungojerrie and Rumpleteazer...who work for Macavity. She smelled him on them!
Why is Macavity able to teleport in the 2019 film? Because he breaks EVERY human law, including the laws of physics (the original poem specifically mentions that he "...breaks the law of gravity", so his breaking others wouldn't be out of the question).
Macavity, He's broken EVERY human law? HMM... Just how literally do they mean EVERY?
Especially as some would be bloody hard for a cat... how, for example, would a cat commit white collar crimes?
Simple. Macavity is JUST THAT DAMNED GOOD.
It's not exactly horror, but Mungojerrie and Rumpleteazer breaking a Ming vase, one of the rarest most expensive bits of pottery in the world... It's a surprise they haven't been thrown out of the house...
There's a good reason (which is really a piece of fridge brilliance) that they haven't been chucked out of the house: They're calico cats, and Mungojerrie is male - and male calico cats are exceedingly rare. Perhaps they could just get rid of Rumpleteazer, but the family can't tell them apart, after all.
Not much is known about the Heaviside Layer, other than that the cat who is sent there gets to be reborn into a new life. Since that usually entails death first, that has some rather dark implications. Even the theories listed on musical's wiki tend to be disturbing.
One of them is that being sent there is a ritual sacrifice, that the cat who is sent there is killed to honor or appease the Jellicle moon. That would mean Old Deuteronomy is deciding which of them gets murdered!
As stated below in the Fridge Logic section, another theory is that the cats are currently alive but are competing for a second reincarnation. If that's the case, what happens to the cats who don't win? Do they just face Cessation of Existence?
In the 1998 stage version, it seems unlikely that Gus (elderly and obviously unwell) will even be alive for the next Jellicle Ball. This is his last chance for the Heaviside Layer trip, but Grizabella (younger and not as sickly-seeming) is the one who gets that new life.
It's implied from their collars and lyrics that some of the cats have human owners. But it's also implied that they're in some kind of purgatory. So are their owners humans who are also in purgatory waiting to be reincarnated?
The Heaviside Layer is more of a play on the nine lives of cats, and a place where they can be reborn back on Earth, rather than implying they're currently in purgatory.
Upon finally getting a chance to see the 2019 filmnote No member of my immediate family has seen the play, I noticed something odd: all of the backgrounds are scaled for humans, not the cats themselves, including the milk bar. Even assuming that the story is set in the Prohibition Era, how does a milk bar makes sense for human customers? Wouldn't an ice cream parlor make more sense?
tend to be disturbing.