You don't hear the term "liniment" much anymore, but it seems like basically the same stuff as Ben-Gay, Icy Hot, etc.
Sometimes you come across it reading classic books. Does anyone else remember the scene in "Anne of Green Gables" where she puts liniment in a cake?
Her foster mother had put liniment (homemade, I assume) into an empty bottle labelled "Vanilla Extract." Anne used it in the cake. The poor lady she served it to was too polite to admit there was anything wrong with it, and Anne was too nervous about having company to taste the cake herself!
I'm imagining a cake made with something like Ben-Gay. Yikes! I'm assuming Anne's form was more liquid than what you see today. It would be hard to mistake Icy-Hot for vanilla. But if it was alcohol-based (like vanilla extract) and thin, I can kind of see doing it.