The final retiming step makes sure that the head motions follow the speech correctly.
最后的重定时步骤则确保头部运动与语音同步。
两分钟论文
If you have any doubts whether this is required, here are some results with and without the retiming step.
如果你对这一步骤是否必要有疑问，那么请看看这个，这里是一些无重新定时效果的比较。
英语百科
Retiming
Retiming is the technique of moving the structural location of latches or registers in a digital circuit to improve its performance, area, and/or power characteristics in such a way that preserves its functional behavior at its outputs. Retiming was first described by Charles E. Leiserson and James B. Saxe in 1983.