The relation between verb 打 (hit) and object 这个学生 (this student) is clear to indicate sentence S2 is an Attack event mention since the object is a person, while object 电话 (phone) in sentence S3 is not a person and it indicates this sentence is not an Attack event mention following the sense of verb 打 (call).
the object is an effective evidence to indicate event mentions and it is incorporated in our model to remove pseudo event mentions as follows.