This evening, while checking my mare's vulvar area, I noticed a small marble-size water blister-type looking 'thing' inside of her at her inside opening. I have not ever seen anything like this before in a pg mare - it is not the bag, as she is not in active labor. She is showing many signs of impending foaling, however, and lost her mucous plug last Sunday morning. She is at day 315. Curious to know if anyone has ever seen something similar and might have any ideas. I do have some theories floating around in my head LOL