Suppose that aliens from another planet decided to visit your house and make contact. Let's also assume that the aliens spoke a different language. How would you break the language barrier and communicate an idea to them?
Many concepts that we've developed as a species are abstract, as they don't require a physical example. However, we often use physical objects in order to explain what counting is. I suppose my answer to this question would be to start by associating numbers with objects and then going from there. I would only hope that they would get what I'm saying when I group certain objects together, as counting 2 things is not the same as counting 2 of the SAME things. If one could get them to distinguish between the two, that would be an encouraging sign that they're understanding our thinking.