Adds a Hair Bunch constraint to the selected hair curves. This can help create body to the hair as it animates in a fashion similar to self collision, but with much less computation. The initial set of points nearest the constraint will repel each other where they overlap (according to the clump widths). There is also a slight static cling where the points stick together slightly when they touch. If the hair clumps overlap at the start frame they may suddenly push apart (unlike the other methods, which have no force at the start of a simulation). You could run the simulation until it stabilizes then set the Start Position to handle this problem. See Set up hair constraints.