One of our ewe lambs from last year has an odd habit, occassionally she opens and stretches her mouth a lot as if she is 'singing' but with no noise (imagine you are miming along to an witney houston number and you get the idea). Sometimes this happens after she has been fed but not always.
Other than this she acts just like the others and is fit and healthy. I don't notice this behaviour in any other sheep. any ideas what this could be?