@freemo @xyfdi There was that Greek King, that married his sister, who built up a degree of immunity to common poisons by ingesting them. Snake farmers also can build a degree of resistance to snake venom by getting bit by the snakes.
The human body is fascinating.
Doc Freemo 
@xyfdi While obviously an absurd idea, it actually works with more things than you might think (not that its smart given safer alternatives)... like this works with biologically complex poisons (building up an immunity through small doses over time).