What does the narrator learn in these lines?

How could I have confused my grandmother’s voice with that of a bleating goat? I felt terribly guilty and ashamed. I knew that the shed door was prone to latch by itself if it was slammed. That’s why a wooden stake for propping the door open was usually kept nearby. But this time the stake had not been used, and now my grandmother was shaking and shivering and glaring at me.