Not to get knee deep in the weeds, but the issue of Euphorbia sap as a poison/toxin is a bit of a misunderstanding, at least insofar as we gardening humans are concerned. Poisons/toxins are generally things that make you sick when you consume them (unless they are the type that can pass through skin or air or whatever). The principal danger from Euphorbia sap is unrelated to its effects should we consume it. Euphorbia sap is a very potent irritant, meaning it can irritate the skin, mucous membranes (nose and mouth), and eyes to the point of causing extreme pain and prolonged rash-like effects, even blindness in extreme cases. The irritant effect is what will make you sick if you come in contact with fresh sap and don't take care to avoid it. The irritant effect is what is most likely to send you to the hospital, unless of course you eat huge quantities of a plant (in which case you'd probably still be pretty sick from the irritant effect before anything else kicked in). The irritant effect is local, affecting those parts which came in contact with the juice.
Fun fact: some Euphorbias are actually known to be edible (to some livestock, anyway) and these have names like esculenta ("edible") aka Soetvingerpol (roughly "sweet finger plant").
Euphorbia (Euphorbia esculenta)
In my experience several succulent Euphorbias are not actually toxic or poisonous or even necessarily bad-tasting to very hungry hares, gophers and squirrels. Whether or not they are poisonous to humans is another matter, but you can be sure that whatever toxicity exists, it varies widely from one species to the next. For what it's worth, based on the aforementioned hares, E. mammillaris is on the nasty/bad-tasting/toxic side, because the hares completely ignored it while devouring the polygona right next to it.
