Slip It In is an extension of the sound Black Flag utilized on its second album My War: heavy, cathartic, intense, dense and progressive. The album pursued the newer, lengthier song arrangements that Black Flag would develop until its demise. It also features Henry Rollins' further development as a lyricist, contributing four of eight tracks on the album. This album also demonstrates Black Flag's increasing use of instrumentals, where Greg Ginn demonstrates his increasingly more complex playing style.
