Does anyone know what's wrong with this bird's foot?

Does anyone know what's wrong with this bird's foot?
Originally uploaded by Cobra_11

This finch was on my seed bowl for the first time this morning. There was some sort of growth on its foot. The growth didn't seem to bother the bird at all. The bird looked healthy and it had a huge appetite.

I also noticed a similar problem on a goldfinch that comes to the seed bowl regularly, but that bird has problems with its feet - the goldfinch can't stand properly.

Does anyone know what this is?