The sexual act of placing ones penis between a pair of hairy butt cheeks - idealy of a female who then farts.
Making the hair tickle the shaft and feeling like the legs of a caterpillar walking.
A couple meet in a bar wanting to try something new and go home to experiment. They are watching animal planet during a series on caterpillars they play around with this bizzare idea of farting on the weaner between the hairy buns... Hence the "Norwegian Caterpillar"