In town to perform on “Saturday Night Live” this weekend (where he hopes to be written into a comedy sketch), Los Angeles rapper Kendrick Lamar visited Funkmaster Flex’s Hot 97 show yesterday. Watch how he twitches his right hand when he raps. It seems like a device he’s developed to help him remember his lyrics. Like some kind of muscle memory thing or something. It’s cool. And he’s really, really, really good.