How does Medicine Work?

Collin had a runny nose and some congestion earlier in the week.  One of the times I gave him some liquid medicine, he asked "Why do I need to take this medicine?".  I said that the medicine will help him to breathe better and stop his runny nose.  He took the medicine and then had this puzzled look on his face.  He then asked, "Mommy, how does the medicine know to go up there?" as he pointed to his nose.  Great question, right?  I told him that the medicine knows where he hurts and where to go.  He was happy with that answer and ran off to play.