I wouldn't have known to try either had I not seen Swen do it during some stream. It makes a lot more sense for poison to be used this way than to be thrown a someone's feet. I guess everyone in BG3 has porous toes.
Have you ever noticed how your body absorbs liquids? We all do have porous toes.
This will be a fun thing to try, at some point though. Even if it's not a playthrough to take out of Act 1.