The glow squid has some overlapping textures around its tentacles. Specifically around the body of the squid. Although the glow squid is supposed to be distracting, I don't think this is what we're supposed to look at.
If you spawn in a glow squid and stare at where the tentacles and body meet, it is very apparent.
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This is the same for all mobs where the leg connects with the body; may be intentional to create walking/swimming animations