Gary, I have to disagree - too fussy and machine intensive. Quite formulaic as placing the pointer in the same position shows the identical effect every time.
As to how it is done - with a shedload of code.
If I was tackling this, I would create the circle around the pointer using a circle clip-path of the under-image.
This is rerun for every pointer travel although I would limit it to around 5px.
The same trick for the triangles for the top-images with a triangular clip-path.
The JavaScript code does the recalculations for the one circle and random triangles.
More code would position and create the triangles.
I found it most distracting.
Acorn
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