I suppose it's worth saying that in Shakespeare's day, 'accuracy' wasn't an issue the way it is now. The days, if you set a film in 1958 and show a car that wasn't made until 1959, it'll soon appear in a book of bloopers. But people were less nitpicky then. Shakespeare mentions chiming clocks in Julius Caesar, as I recall; the Romans didn't have them, but his audience simply wouldn't have cared. My guess is he might well have heard of some poison that works via ears, but wouldn't have done any research whatever to see if it existed.