Complex sentence: The three soon find the Devil's Eye within a pirate skull; as Penny pries the mouth open with a sword, the mice push it out from within, but soon the oceanic tide rises and floods the cave.
Split into simpler sentences: The three soon find the Devil's Eye within a pirate skull. As Penny pries the mouth open with a sword, the mice push it out from within, but soon the oceanic tide rises and floods the cave.