Speak Boris, Speak

We have a Rottweiler named Boris who is very big and oafy (or is it spelled ophy)... anyway, for some reason he was the most difficult dog ever to train.  He is just simple.  He can sit, shake, and lay down, but for some reason the command speak just perplexes him.  So, yesterday we were in the kitchen (me, brian and bailey) and Bri was trying to get Boris to speak.  He had a treat in the air and was like "Speak Boris" and Boris starts to run around in a circle and sit down.  nooooo..."Speak Boris."   He runs over to bailey, steps on Bay's toes with his tallons (gigantic nails) and sits down on bay's feet.  Noooooo, ..."Speak Boris."  He comes over to me and nudges my hand.  Nooooo..."Speak Boris"  he lays down.  "Wait," I say, "Let me show him, I'll speak and you pretend to give me the treat."  Brian, "Speak Jenn, Speak"  Me:  "Wooooooffff".....Brian "good girl"  Pretends to feed me the treat....All the while Boris is watching us....Good try it again.  Brian, "Speak Jenn, Speak" Me: Wooooooffff.....Brian "good girl" Pretends to feed me the treat.  Okay B, your turn, ..."Speak Boris" He runs out of the room and doesnt come back... Brian looks at me..."He left."  End of Speaking lesson.