Scars of Dracula

Soon afterwards, the local villagers are enraged that yet another young woman has been murdered by the Count. With a priest's blessing, they rise up and set fire to Castle Dracula. However, the Count is safely asleep in his solid stone chamber, When the villagers return home, they find that every single woman and child in the village has been slaughtered in the church by bats.
Falsely accused of rape by the burgomasters's spurned daughter, libertine Paul Carlson flees the Kleinenberg authorities by jumping into a nearby coach which, though driverless, heads off at great speed. He is deposited near Count Dracula's mountaintop castle. Initially he is welcomed by the Count and a beautiful woman named Tania, who later reveals herself to be imprisoned by Dracula as his mistress. Paul later has a liaison with Tania, who concludes their lovemaking by trying to bite his neck. Dracula enters and, casually throwing off Paul's efforts to stop him, savagely stabs Tania to death with a dagger for betraying him. The vampire's servant Klove dismembers her body and dissolves the pieces in a bath of acid. Locked in the room high in the castle, Paul uses tied-together bed curtains to climb down to a lower window, but the line is withdrawn by Klove, and he finds himself in the Count's chamber.
Paul's more sober brother Simon Carlson, and Paul's fiancee Sarah Framsen, come searching for him. A maid at the tavern directs them to the castle and they investigate. Dracula immediately has designs on the lovely Sarah, but Klove, who has fallen in love with the young woman after seeing her photograph amongst Paul's possessions, helps the young couple escape by refusing to do Dracula's bidding and remove Sarah's crucifix. The servant pays a terrible price for his disobedience as he is sadistically burnt by Dracula with a red-hot cutlass.
Simon, having enlisted the help of the village priest, goes back to the castle to look for his brother. However, the priest is attacked and killed by a large bat, and Simon is betrayed by Klove, ending up in the same locked room as his brother. Opening the coffin in the middle of the room, Simon discovers the sleeping Dracula, but the vampire's power reaches through his closed eyelids, causing the young man to collapse before he can take action against the Count.
When Simon recovers, the vampire has vanished. Investigating the room further, he is horrified to find his brother's drained corpse on a spike. Looking out of the window, he is amazed to see the Count running up the wall outside like an insect. With a rope let down by Klove, Simon climbs up the sheer outer wall to go after Sarah, knowing that Dracula may use her as his new mistress.
Sarah, meanwhile, has made her way back to the castle battlements as a storm approaches. Suddenly, she is confronted by Dracula, who this time uses his bat familiar to remove her crucifix. Just then, Klove arrives on the battlements and attacks the Count with the dagger the vampire used to murder Tania, but the servant is hopelessly outmatched by the vampire's inhuman strength and is thrown over the side of the castle.
Simon arrives and throws a heavy iron spike at Dracula with the intention of staking him in the heart. The spike pierces the Count, but on the wrong side of the chest. Unharmed, Dracula raises the spike to impale Simon, but the spike is struck by lightning and Dracula is immediately engulfed in flames. Staggering in agony, the Count collapses and topples over the castle's battlements, falling to the ground far below, where his corpse continues to burn fiercely...

Question: What strikes the spike, engulfing Dracula in flames?
Answer: Lightning