Because he's prone to tail rubs in the summer, I sometimes pick up his tail and check the underside of the dock. He's had small sores there before (usually what instigates the rubbing) that have required some treatment.
That night, I found this.
It's about the size of a gumball, hard, and not sensitive. I have no idea how long it's been there. Maybe all summer.
I fretted for a moment, and then used the wonder of technology to email my vet and include an image of the lump.
I fussed over him for another 30 minutes or so, rode, and then worked on his feet. By the time I got home, I had an email back from the vet: she wanted to come biopsy it ASAP.
So, while you're reading this post, I'll be at the barn meeting the vet, to biopsy the lump.
It's either an abscess (from afore-mentioned tail-rubbing) or a melanoma. The latter is more likely. The biopsy will tell us what kind it is.