I'm uploading this photo under a separate heading, as well as the previous thread, for information/reference purposes. This is Basil's foot before he went to the vet. The lump was quite hard and shiny and not a domed sort of shape as you might expect an abscess to look. When the vet lanced it, it had a small, quite thick, feather curled up inside and a lump of hard, cheesy pus (yuk). Basically the feather follicle had become infected which was causing him to limp - which was a good thing as otherwise I would never have noticed it under all those feathers. The large hole it left behind was washed out with hibiscrub and he is now on 8ml Baytril for 3 days, but seems absolutely fine.