The world’s richest man, Elon Musk, is facing a new obstacle in his bid to buy Twitter. On Friday, Twitter’s board of directors adopted what’s known as a “poison pill” to thwart Musk’s $43 billion hostile takeover. The move could allow existing Twitter shareholders to buy additional shares at a discounted price. This would dilute Musk’s stake in Twitter and make it more expensive for him to buy the company.