Oh, wait, on second look I have to take that back. My apologies. It is a part of the spline interpolation, but I can't tell you from the top of my head what exactly it's doing in there. But I'd guess the fact that it's set to 1 all the might indicate that there's a good reason behind it. After all, there's a reason why jointMult is set to 1 (try setting it to 10 to find out why...)