I think a yawn reminds us that there's another person there with feelings, emotions etc and we're suddenly very aware of how much we want T's attention, caring and we become ashamed suddenly of those desires and when we feel shame we want to hide/withdraw. If we were to put into words how T's yawn made us feel it wouldn't seem nearly as bad as the back and forth internal arguing we put ourselfs through, and the unconsious anger it triggers would vanish.