Cobras, taipans, black mambas — Tim Friede's been intentionally bitten more than 200 times by some of the most venomous snakes on Earth.

And he survived, mostly because years of self-injecting venom let him develop immunity to them.

(Please do not try this yourself!)

Now his blood's been used to make a broad-spectrum antivenom that researchers say may protect against nearly 20 deadly snakes.

But this is not how antivenom is usually made. So how are snake antivenoms produced, and where are we with a "universal" version?