I was scratching my hand then suddenly part of the vein started to swell, now there's a blue lump on my hand, like a gorge of blood in one part of the vein. I'm not particularly worried, but I'm interested to know what has happened here. It's quite sore to prod at (so as my flatmate said: "don't touch it then!"), very bruise like, though I didn't bang it off of anything.