How does the Thundershirt for cats work?

Mickey in a Thundershirt.
The manufacturers of the Thundershirt claim that it works in the same way swaddling a baby works. I am not sure that this is true. The Thundershirt works for cats and dogs. I believe that the reason why it works for a lot of dogs may be different to the reason why it works for a lot of cats. I get the impression, by the way, that the product was created initially for dogs.
I am making the point by the way that its effectiveness will vary. It may vary quite a lot for cats because this product does not calm cats so much as zap them. It has a similar effect to a drug on many cats. There is a definite alteration to the mental state of the cat. The cat can look bemused and a bit confused. Cats stumble sometimes at least initially but they get used to it somewhat. Also cats can become slightly more affectionate. I think that is a fair observation.
They can lose their athleticism. They may flop off the bed rather than elegantly jump off and so on. It can affect coordination. This indicates that this is not so much a calming effect but an alteration to the mental state of the cat. For dogs it may have a calming effect but I have not observed dogs in Thundershirts.
All those things said, I like the product when used under certain circumstances because it can be very helpful.
But what is happening? How does it work? The pressure from the Thundershirt appears not to trigger the same emotional response as for babies in swaddling. Swaddling of babies is meant to replicate the feeling the baby had when in the womb. This is reassuring; hence the calming effect.
Putting pressure on a cat with a close fitting harness zaps the cat as mentioned. It can semi-immobilize a cat. I see a cat behaving as if on a tranquilliser. A possible reason why this happens is because the cat feels to a certain extent that he/she is being carried by her mother by the scruff of the neck. We know that this activity immobilizes cats. It is designed to do so as it allows the mother to transport her kittens to a new den unhindered by a struggling baby.
Therefore I would suggest that the Thundershirt works by replicating to a certain extent (i.e. not completely) the process whereby mothers immobilise their young when transporting them in their mouths by biting gently down on the scruff of the kitten’s neck.
How can the Thundershirt achieve this? I believe that it is a combination of the collar of the product pressing down on the rear of the neck and the pressure of the Thundershirt on the torso which tweaks the cat’s nervous system in such as way that the cat receives a similar signal as when being grabbed by the scruff of the neck.
An alternative theory is that we know that cats love boxes. They like to squeeze inside boxes. This puts pressure on their body where it is in contact with the walls of the box. This reassures them. The reassurance and calming effect may originate in the close – almost pressed together – contact very young kittens have with their mother and litter mates. It is feeling which is a throwback to when they were newborns.
This theory is more consistent with how the Thundershirt works for dogs too. For me, the bottom line is that something fundamental happens to the cat’s mental processes beyond simply feeling reassured in the same way cat owners reassure their cats with stroking for example.
Do you have a theory? Have you read about how this product works other than from the manufacturer?