Hoppin' and Cawin'

The other day, someone in my Crow group (Facebook) referred to crows as hopping.  Crows are rather large birds, and most large birds don't hop.  However, I did read about a magpie hopping, which is a cousin to the crow.  Well the other day, I did see a crow hopping.  It was hopping in a tree among the leaves from branch to branch.

This crow was expressing vocals and I found myself wondering if there was a pattern to its calls.  The crow expressed several series of AH sounds.  Sometimes they came 4 at a time, one right after the other.  Sometimes it was 5 in a series.  One, maybe two times there were 3 in a series.  It seemed that 4 AHs in a series was expressed the most.  But why?  What does 4 AHs mean?  How do 4 AHs differ from 5 AHs?  Why was 4 AHs expressed the most in the time I was observing the bird? I didn't notice anything unusual about the AHs.  No one AH sound was dragged out or was expressed in a harsh manner.  The crow went back and forth in regards to the number of calls in a series.  (Sometimes it would be several instances of 4 calls in a series, then 5, then back to 4 and so on.)