Black bumps on chicken comb

[GRB73]

What are these black bumps? My hen usually has one or two but they have multiplied overnight. At first I suspected fowl pox, but they were never yellow. Just black, and they appeared since yesterday. No other symptoms. Thanks.

 

[CaliforniaMountainChicks]

It looks like blood from being pecked in the comb or scraping it on something. Do they wash off?