I don’t know what “fossilized algae” refers to

Looked it up:

Nobel found that when nitroglycerin was incorporated in an absorbent inert substance like kieselguhr (diatomaceous earth) it became safer and more convenient to handle, and this mixture he patented in 1867 as “dynamite”.

Diatomaceous earth consists of the fossilized remains of diatoms, a type of hard-shelled microalgae.

https://en.wikipedia.org/wiki/Alfred_Nobel#Nobel_Prize

https://en.wikipedia.org/wiki/Diatomaceous_earth

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Maybe sounds like the art from Fantastic Planet?

Probably not in the way you mean. There are certainly movies that benefit from watching again, whether to fully understand what is going on - often involved convoluted plots or a twist that adds new context to all the scenes, or because each individual shot/scene has so much going on that you’re always catching some new detail. And I do think those aspects are mostly intentional.