Yet Another Stupid Question: WHAT Is This On His Flank??

[Brigid]

@RPM

I didn’t suggest it might be a tumor; I just said it looked sort of like one. To me, who has seen only one outside-the-body tumor, and that was on a mouse 50-odd years ago.

ETA: I don’t think your question was at all stupid. I’m just as curious as you are as to what we’re seeing there.

THANK you! I’m glad you see it as well.

[GoodTimes]

I would bet money that it’s just a wrinkle. Google images of racehorse and you’ll see that when they reach that far underneath themselves that everything bunches up near the stifle.