Hardish lump/bump 5" below hock

[Corona]

On a liveries horse. What could this be!? Its about the size of half a grape (if you cut a grape in half and stuck it to her leg) feels pretty firm, but if you squeeze it, it does give a little, feels almost like you could slide it, like a pocket or something, quite strange. No heat, no lameness. Any thoughts?

 

[touchstone]

My first thoughts would be a curb, but I would have expected to see some soreness with that, unless it is a false curb?