This 'snake venom' theory is from > 1y ago. McCullough commented on that. Some pp think it is an intentional distraction, a false flag operation. Discredit the true conspiracy theories with an exagerated one, a common tactic.
Both snake venom and spike cause clots. there are some similarities on chemical processes. But there are also many other stuff that messes with the blood in similar ways. It appears to be just a bogus comparison.
auto-immune: any mRNA vaxx is supposed to cause auto-imune issues.
the vaxx instructs the cell to produce a foreign protein.
the protein goes to the outside of the cell membrane
defense cells recognize the cell with attached foreign proteins as foreing, 'non-self', and kill it = auto-imune disease.
that is one of the basic and first proposed mechanisms of harm for the mRNA tech,