Look this up on Google. Bulldogs are known to have some strange head and facial movements that are related to myotonia. No one knows exactly why. Jammy had her first episode a few months ago. It does happen when they are active/playing. Sometimes just putting a hand on her or petting her makes it stop. I'm a dr and it really freaked me out the first time. I can only imagine how worried you've been. It doesn't affect their quality of life or life span. There are some people who believe it has something to do with allergies, but there is no medical research that supports this. I hope this helps.
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