Hi John...thanks,
At 4:29...I said "Bong" (it's hard to put into English = Cantonese words anyway)...haha You would know better then me.
But in Hung Style Bong Sao is not just a block...it can be used as a Wing to break or disrupt someone's structure. In this case we use the Bong sao to "Separate or Divide" at the elbow.
In that instance..the key element is holding his left arm out so that it is "Extended or LONG".
What is important is the ability to "follow" the energy of my opponent. If I pull his left arm to make it LONG and he resists me....then I Follow his resist and counter his technique in the same way he is fighting me.
"O"