Complex sentence: Shift Supervisor Jack Godell (Lemmon) notices an unusual vibration while grabbing his cup of coffee which he had set down; then he finds that a gauge is misreading and that the coolant is dangerously low (he thought it was overflowing).
Split into simpler sentences: Shift Supervisor Jack Godell (Lemmon) notices an unusual vibration while grabbing his cup of coffee which he had set down. He then finds that a gauge is misreading and that the coolant is dangerously low (he thought it was overflowing).