English Grammar : article, syntax, verbs conjugation, English spelling

An object complement is an entire noun phrase that acts as the object of the verb: “She said that she was sorry.” “...that he was sorry” is the object complement of the verb “said.” That is, the phrase “completes” the meaning of the verb “said” by telling us what “she said.” In colloquial speech, the object complement can replaced with what to form a question: “She said that she was sorry.” “She said what?”
“He thinks he knows the answer.” “He thinks what?” The most common verbs that have object complements are “stative verbs,” verbs that show sensory perception, mental perception or emotion:

Sensory Mental Emotion
see know want
hear think desire
perceive say
appears assume
Object complements are often introduced with a complementizer. The common complementizers are that, for (which introduces a noun + infinitive complement) and possessive pronouns (which are followed by the -ING form of a verb). “He heard that we went to the play.” “He planned for us to attend the play together.” “He anticipated our coming to the play.” In conversation, the complementizer “that” is often left out: “He heard that she went to the play.” “He heard she went to the play.
“She said that she was sorry.” “She said she was sorry.”