On Tuesday I was feeling along Lacey's back (in relation to her nickering/whinnying when I dismount) and I noticed that right over her loin/point of croup (technical words I looked it up, haha) she has a rather largeish bony feeling bump. It's not super obvious or anything but it's definitely noticeable when you run a hand down her back kinda hard. I've never noticed it before but I wouldn't doubt that it's been there...
What could it be?
Here's the bump:
And here's its relative location (the blue circle):