Bleeding?

So, I've decided to try and breastfeed my boy when he's born. I tried 13 years ago when I had my daughter but I was convinced she wasn't getting anything so stopped. However, I saw a video today of a woman pumping and there was blood coming out with her milk and when she filtered it there was a large stone looking thing in there. Does that actually happen? Trying to not be put off by it but iys playing on my mind 🙈