I would appreciate if someone could explain the concept of what a mirror trade is, specifically in reference to a MM. MM not filling your entire order but keeping half for himself and filling half of your order. I ask as I have read that when mirror trades are noticed on the time and sales -it is a positive sign and that someone is most likely accummulating shares. How does someone spot that mirror trades are happening? Specifically, that another trader didn't by chance just place the exact same trade as another trader?