There's also the "Psychic phenomenon" explanation for things like that and UFOs, which itself can be broken down into two separate camps.
- Something extradimensional is leaking into this reality, as you said
- We are perceiving something "real" but that our brains can't properly resolve, so we go with the closest-neighbor to our understanding
On that second one, the idea is like when you can't resolve an image you haven't seen before until it's pointed out to you, or you look at it a certain way and then "can't unsee".
View attachment 3740953
This is a Dalmatian sniffing the ground facing away from the camera.
It's also kind of like how the "questing beast" from Arthurian legend is described as "The strange creature has the head and neck of a snake, the body of a leopard, the haunches of a lion, and the feet of a hart."
Or the Beast of Gévaudan, which is described thus: “the size of a very large wolf, the color of burnt coffee, with a black bar on its back, a dirty white belly, and a very large and plump head.”
You can only really describe things in terms of what you have already experienced and understand, but if you see something super-weird you can only describe your impressions or split-second understanding of the thing.
This phenomenon is also thought to possibly be behind the Green Children of Woolpit.
According to the legend, around the 12th century, strange, very young, green-colored children were discovered near the village of Woolpit. They were dressed in bizarre clothes, spoke a bizarre unknown language, and refused to eat anything until they were given raw beans which they ate immediately.
One of the children died, but one of them, the girl, survived, eventually lost her green coloring after getting used to eating other food, and learned to speak English. She claimed that she, and her now deceased brother were from some place called St. Martin's Land where the sun never shone, and where they had been tending to their father's cattle when they heard a loud noise, and suddenly somehow ended up near the village.
In reality, these children were most likely the kids of Flemish clothworkers from the village of Fornham St Martin who had fled the carnage of a battle that had recently taken place there.
Their green coloring came from them malnourished due to them wandering in the woods for several days with no food which is also why it eventually went away after they got a better diet than just raw fucking beans.
Speaking of beans, the reason they only ate that, and nothing else is most likely because it was only the food they actually recognized. The children were very young after all, and if you've ever had to try to get very young children to eat something they don't recognize, or immediately like, it can be an incredibly annoying, and difficult task. Yes, even if they're literally starving. Kids are like that.
Lastly, their odd clothing is just them being dressed in traditional Flemish clothing which would've been unfamiliar to most English peasants at the time, and them being young, traumatized, frightened, children who didn't speak English, and were too young to fully comprehend nor explain what had happened to them clears the other shit up as well.
Or you know, they could just be magical creatures from another dimension. That works, too.
It certainly did for the villagers of Woolpit.