Slip It In is an extension of the sound Black Flag utilized on its second album My War: heavy, cathartic, intense, dense and progressive. At this point, Black Flag was considered by many to be one of the leading bands of the American punk scene.
The closest punk rock came to spoken word Jazz? Rollins shpiels on side A, Black Flag improvises on side B. If you jazz and punk and Rollins, check this 1984 classic out.