Musk announced that his infrastructure firm had started selling flamethrowers Sunday. People were able to pre-order them for $500 each, and could buy an "overpriced" fire extinguisher with a "cool sticker" for $30 as well.

After a successful run selling hats , billionaire Elon Musk's The Boring Company has expanded its offering to include flamethrowers.

The entrepreneur, who is also the CEO of car manufacturing firm Tesla and aerospace firm SpaceX, said Monday that The Boring Company had sold 7,000 flamethrowers. That means The Boring Company has sold at least $3.5 million worth of its new product.

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Musk's idea to start selling flamethrowers began as a joke in December, when he said that if his company sold 50,000 hats, it would start selling flamethrowers.

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The billionaire posted a video to his Instagram account Sunday where he was seen wielding one of the weapons and charging toward the person filming him.