North of the Frozen Tundra, but I can see it from my house.
At noon today my 6 yo filly greeted me with a smile. Her upper lip was pulled up, showing me her pearly whites. I took a few photos of this, as it was cute. It became less cute however, when she continued to flehmen (smile) in my general direction, and didn't want to eat hay or even sugar. She was not exctending her neck while she did this, as a horse might from an odor, but just watched me calmly, smiling and not eating, as I went about the barn. I have not seen this before. She is fine now.
Has anyone else seen this? A text with photo to my vet has not yet been returned. Maybe she was bitten by a bug? She is fine now, but it was weird.
In my experience it's often related to some minor pain somewhere. Be it a little intestinal gas pocket or when given an IV, mine will flehme to say, I'm a little outchy.
Mine also flehme when they smell weird things, but like you say, they'd be extending their necks, doesn't sound like your filly picked up on a weird sent.
She could have had a little intestinal cramping from some minor gas that went on its own fairly quickly.
Considering she's acting normal again I wouldn't worry too much, but just be observant like you are.
If it happens more frequently, ulcers is a possibility, but than again she's seems a little young for that.
I know a horse who does this as one of his only pain indicators. During a recent colic episode the farm vet thought his presentation was rather mild, but the horse's continual flehmen response didn't set well with the owner, and he was soon shipped to the veterinary hospital. He collapsed a few hours later and went in for surgery.
You know your filly best and know if this is just a sense of humour or perhaps indiciative of pain. Perhaps she's just being a ham!