Plaster?

This afternoon I stopped into a shop in Vysehrad park to check out the wares. Shortly after being greeted in Czech by the shopkeeper, I hear him mumbling something in pain just outside the back door. Next thing I know he is sitting at the desk with a small white box in hand and saying something about plaster. I'm thinking plaster... really? He looks at me and says "in UK you say plaster." (Seems he thought I was from the UK). After closer inspection of the box, I looked at him and replied "in the states we say band aid!"