Continuity: When Gran first dangles down from the ventilation shaft, the slaver's key ring is too wide to fit through the opening. But when Jim loses his balance and Gran is jerked back into the cell, the key ring is suddenly much smaller than before.

Plot hole: Major plot leak: How could Flint's ship get into the lake atop a tall volcano all in one piece? If he wanted to merely hide the treasure in order to recover it later, the whole setup, including the lake's draining system, would be totally unnecessary, and it looks all too deliberate for the ship to be sitting in the lake by accident (say, thrown in by a violent storm).

Other: The sign which Silver reads says that one's got ten seconds to get away after pulling the chain. But in fact, after the monkey pulls the chain, fifteen seconds pass before the detonation (I've been counting).