Jon Davison of Yes and Taylor Hawkins of Foo Fighters are buddies from high school, so when the Fighters were in town,
Davidson was brought on stage to sing Tom Sawyer, which the Fighters have been covering this tour. Taylor is wearing a Yes/Chris Squire shirt. There's a funny bit about them trying to learn a Yes song really fast, but it was "too f****** hard."
On a totally unrelated note, the great Nate Mendel of Sunny Day Real Estate and Foo Fighters is on bass, as always.
PS. It's Foo Fighters, so there's NSFW language.