Cavalary: Depends where you are I guess, from you two I gather it's referred to in an entirely different way in Poland. Here it's called "booster" by everyone, including officials, they didn't try to find a way to translate that.
Yes, indeed, we have our own Polish name for that. :) That's a part of misunderstanding for sure.
Just like I didn't know what exactly "be square" means. But at least "be square" sounded as some weird "combination" of words so I googled for it. In case of "booster shot" at first I thought it was something connected to these "cat game stories" I was reading about earlier. Now all I can say is it was really stupid connection that came to my mind. :D