README to users of subject S9 data

Warning for the users: All signals (motion, forces/torques, eye gaze, videos) were collected uniformly among subjects, including S9. However, as explained in the article, some technical difficulties in the day of experiments with S9 left available only one method to synchronize the signals: the detection of the precise instant in which the subject picked up the utensil from the table, which was a very evident event in the signals. So, the signals’ synchronization method is the only difference in S9 with respect to the other subjects. Even if this difference is not expected to cause a significant bias in the data, users are advised to pay special attention to the data from these trials.