Jet and Kilt don't need "bite work" in their infinite wisdom (aged). We thought Yoko had a bug or something in her ear when she came off the field with the range ewes at the last trial. Our success was she got them lifted. But, I'm surmising she got "clocked" a good one at the top. Her ear was red and she was shaking it violently.
As noted, this little pup is a heeler. I have just started some bite work with her. I put a few sheep in a pen and called her into the pen. I watched her reactions. First reaction...nail them when they aren't looking on a back foot. Second reaction when faced....nail them on a front foot. Yikes...now that will get you in trouble. And, I bet that's how she lifted them when they all stared her down. And, I surmise that is how she got walloped by one in the head.
When confronted with a face if they don't turn, she will growl. Just a lack of confidence, I'm sure. We will "slowly" work with her this summer and see if we can't boost her level of confidence. And, her parents and I will show her when confronted, where the best place is to bite!