Is “Say Man” history’s first rap song? Probably not - there’s not the slightest effort to sync Bo Diddley's delightfully weird insult routine with Jerome Green to the classic Diddley rhythm. But in the early days of rock, every new idea or modest tweak seemed like it could open a door to a whole musical world. You can likewise hear realms being discovered in the in-your-face slapback reverb on “Love Me,” and on “Shout”’s breakdown (and build up) for the ages.