When you make pig blood more acidic (like adding lemon juice), it grabs onto carbon monoxide gas more easily — but only up to a point. Once it’s super acidic, it doesn’t grab any more gas than before.

Scientists found that making blood more acidic (lower pH) from normal to a bit more acidic made it easier to saturate with carbon monoxide, but making it even more acidic didn’t help any more — just like the claim said.