OK...
After posting this thread I heard my neighbor doing some yard stuff outside the window so showed the bottle to him.
Well, he took one look at it, said he was a legit Scot by blood, and boy was he glad he could intervene in time.
Apparently there's a group in Scotland that makes this stuff who are like a rebel group. They're still pissed about Richard the Second gettin' all pushy back in 1385, so they developed a special kind of poison that affects only people with English blood. And they've been sneaking it into shipments of this bottled stuff---apparently it's for drinking---for a while now.
Well, I've got a good bit of English going back a long way, so thanked him for saving my ass and told him he was welcome to the bottle since he wouldn't be affected by the poison.
I swore I saw a glint in his eye as he took it along with a little chuckle, like something he didn't believe would happen actually did, but I figured he was just relieved to know his neighbor was smart enough to ask about a mystery bottle before doing anything WITH it. Discovering that people in general aren't as dumb as you thought DOES make a person smile, doesn't it?