That's odd (to me)

Hi all & Merry Christmas! I had a quick ?.
When I removed my last sensor, it left a black mark (Idk what it is). Is it a bruise or a bursted vein maybe?

Probably something like that. Keep an eye on it. It happened to me once as well.

It's not super uncommon. Think of it like a bruise, where there was a bit of blood near the surface at insertion time. For me, they always go away within a couple weeks.

If you reuse the same spot, just be sure to move it a bit away for the next time.