We used an finger pulse oximeter and MRI data of the superior sagittal sinus to find reference time frames for the zigzag pattern. We found that the zigzags always appeared during the arterial inflow phase. The abrupt end of the zigzags were coincident with the end-phase of the arterial pulse as shown in Figure~\ref{372115}A and the rise of venous outflow as demonstrated in Figure~\ref{372115}B. 