Many verbs refer to feelings—for example, bore, confuse, excite, frighten, interest. The present participles of such verbs, which end in -ing, and the past participles, which end in -ed, can be used as adjectives (36d).

Use the -ed (past participle) form to describe a person having the feeling.

The frightened boy started to cry.

Use the -ing (present participle) form to describe the thing or person causing the feeling.

The frightening movie gave him nightmares.

Be careful not to confuse the two types of adjectives.