The present study focused on a "tacit knowledge" on agitating motions in cooking. The study observed human agitating motion conducted by an expert confectionery hygiene mistress and non-expert female students. Mixing (whipping) state of fresh cream was evaluated by an overrun which indicates the amount of gas phase and rheology of fresh cream. In the motion analysis, three observation points were set at research subjects' elbow, wrist and whisk. Mixing behaviors were visualized by food red and recorded by a high-speed camera. The expert confectionery hygiene mistress accomplished a peak value of the overrun in two times shorter period than the non-experts. In the non-experts' motions, all motions of elbow, wrist and whisk were strongly synchronized and the time series of displacement showed relatively simple periodic motions. On the other hand, in the expert's motions, phase difference of motions among elbow, wrist and whisk was observed and the time-series of displacement showed to be rather complex and chaotic. Furthermore, it has been found that the expert agitates with small motion putting snap on the whisk.