This is what I think of in class.

Is it possible that we can hear sounds that we really can't.  I mean we can only hear things in a range of theories.  But that doesn't mean sounds outside of that range don't exist.  (By "sounds", I refer to any wave that passes through space by means of vibrations in the air.)

So, maybe those sounds do pass through our ears.  Perhaps it is simply our minds that decide not to process them.  But those sounds might subconsciously affect our thinking.