Oil disolves molecules at the surfaces of materials so they flow out of each others way. Pressure at the knife's cutting edge causes heating of the material. The heat causes the material to loose strength and separate. The motion of the molecules in the knife's edge is what actually does the cutting. The force applied by the knife is concentrated to a small area along the knife's edge.
Rip currents are short lived.
When motion stops swim to shore. Wave your arms and call for help. Swim parallel to the shore until you are out of the current. Then swim to shore. Take the shortest distance path back to shore.