Someone once told me McDonald's doesn't actually use 100% beef, it just comes from a supplier named "100% Beef", and although I'm sure it's apocryphal, I want to believe it.
@Elizafox BEEF is actually an acronym. Barely Edible, Extremely Flavourless.
(I jest.in the UK they legally have to by advertising standards actually use 100% beef and abide by their claims, plus they source it all from british farmers apparently. They're...not terrible? But cow farming in general is bad for the environment apparently :/ )