Creepy Hand Shake

My neighbor friend (a gal) went to a new church with me.
As we were going out the door, a well dressed woman shook my neighbor's hand, it was a long hand shake as she greeted the two of us, and spoke with my neighbor briefly with friendly chit chat. Later, my friend was a little disturbed about what had happened during the hand shake. She said the lady slid her middle finger into the middle of their clasp and pressed her finger against the palm of her hand. She said they finished the hand shake as normal. And she ignored it, but said it seemed very odd to her, and if it were a man that did that she said, she would have had the unction to slap him. After that, the lady walked away and I noticed she did have an awkward look on her face, my friend said, "I felt like she expected me to respond in some way, and that crazy lady realized I had no clue what she was doing."

What the heck was that? Does any one know of a hand shake like that, and what it means between two women?

Is this a secret hand shake, or was this woman just a bird head that makes really bad first impressions?

Please be easy on us we are a couple of country gals just trying to find a good church to go to.