When you find a direct object in a sentence, the sentence is typically written in the active voice. In active voice constructions, the subject performs the action of the verb, and this action is directly applied to the direct object. For example, in the sentence "The cat (subject) chased (verb) the mouse (direct object)," "the mouse" is the direct object receiving the action of the verb "chased."
In contrast, in passive voice sentences, the direct object of the active voice becomes the subject of the passive sentence, and the original subject may be omitted or introduced with a prepositional phrase. For example, "The mouse (subject) was chased (verb) by the cat." Here, the original direct object "the mouse" is now the subject of the passive construction.