Meta recently launched a new app that's a direct competitor to Twitter. It's called Threads, and Meta's Mark Zuckerberg said it has garnered 50 million sign-ups in its first five days. WSJ's Salvador Rodriguez says the new app poses the biggest threat to Twitter, fanning the flames of a long rivalry between Twitter’s Elon Musk and Meta’s Zuckerberg. Further Reading: - Day After Threads Launches, Twitter Accuses Meta of Using Its Trade Secrets  Further Listening: - Twitter’s New CEO: The Velvet Hammer  - What’s allowed on Elon Musk’s Twitter?  Learn more about your ad choices. Visit megaphone.fm/adchoices