The word 吓人 is formed by directly combining the verb 吓 (to frighten, to scare) with its logical object 人 (person). It creates a descriptive compound where the action of "scaring" is inherently directed at a "person", resulting in an adjective-like meaning that describes something as "frightening" or "scary". The formation is a straightforward, intuitive merge of an action and its target to convey a resulting state or quality.