 Staying on the beat is central to rap's flow – many MCs note the importance of staying on-beat in "How to Rap" including Sean Price, Mighty Casey, Zion I, Vinnie Paz, Fredro Starr, Del The Funky Homosapien, Tech N9ne, People Under The Stairs, Twista, B-Real, Mr Lif, 2Mex, and Cage.MCs stay on beat by stressing syllables in time to the four beats of the musical backdrop.Poetry scholar Derek Attridge describes how this works in his book "Poetic Rhythm" – "rap lyrics are written to be performed to an accompaniment that emphasizes the metrical structure of the verse".