Here's the creepy small print.
"If you have open wounds or bandages/casts when you appear, the USCIS may reschedule your appointment if it is determined your injuries will interfere with taking your biometrics."
Really? I don't even know what my "biometrics" are but if I have wounds that are serious enough to interfere with them, I think I might be in the emergency room instead. Good thing this bit of information was offset with a large, bold, capitalized WARNING! or, had I received a biometrically interfering open wound before next Saturday, I might not have thought a thing of it.