one of my hens, suddenly can't walk. She tries to , but it seems as if her legs are paralyzed. She looks alert and is eating and drinking water., but the only way she can get around is by flopping her wings. She has been like this for 2 nights. She is a Silverduckwing English Bantum Her craw seems to be empty although they have plenty of feed. Any thought as to what might be wrong with her would be appreciated. Thanks