My girlfriend's sister is a yoga instructor and she did some private classes with me and my girlfriend. On one session she did a pose where she raised her ass in such a way, I could see through her gray yoga pants and spot the tiniest pair of lace Victoria Secret panties with little flowers on them. I tried not to make it obvious, but I was getting hard every time she bent over and I could see the cute pattern on her panties. About a week later, she came to the house to do laundry and while the girls were away, I had to look at her panties folded neatly in her basket. I found them and a nothing but lacy thongs. Now every time she's over, I can't help but stare at her shapely ass and wonder which pair she has on that day.