Sometime the basic SVO English word order becomes altered when an SVO sentence is interrupted by another structure within the sentence. For example, when a relative clause occurs immediately after the subject of a sentence, the relative clause interrupts the SVO order of the main clause of the sentence. Consider these examples:
The teacher (S) read (V) the book (O).
The teacher (S) read (V) the book (O) which (O) the student (S) found (V).
The book (S) which (O) the student (S) found (V) explains (V) English grammar (O).
The first sentence reflects simple SVO word order because it does not contain any additional structure such as a relative clause. The second sentence contains a relative clause--which the student found--which follows and describes the object, the book. Although the relative clause exhibits an altered word order (OSV), the main clause still exhibits SVO word order because the relative clause FOLLOWS the main clause object.
In the third sentence, the relative clause follows and describes the main clause subject, the book. Therefore, it INTERRUPTS the SVO order of the main clause. As a whole, the sentence reflects the order SOSVVO, quite a deviation from the SVO order of a simple sentence.