We could have alternatively used a bounding hierarchy to accurately handle contacts in all situations. The advantage of our method over such hierarchies is that we can statically compute the processor communication pattern; otherwise, we would need to dynamically update the processor communication or exchange all hair data between processors. The disadvantage of our algorithm is that the contacts may be incorrect in certain situations, such as when long hair is flipped from one side of the scalp to the other. For our production needs, we have run into few examples where this limitation has caused artifacts. In these rare cases, we decrease pruning to guarantee the correct contacts.