Complex sentence: Her struggles and screams awaken Rod, who witnesses her being stabbed by an unseen force, before she is dragged up the wall, her screams alert Nancy and Glen who are unable to enter the room.
Split into simpler sentences: Her struggles and screams awaken Rod, who witnesses her being stabbed by an unseen force, before she is dragged up the wall. Her screams alert Nancy and Glen who are unable to enter the room.