An urgent tone demanding immediate action is a common tactic used in phishing emails to create a sense of urgency and panic, compelling the recipient to act quickly without giving enough time to scrutinize the email's authenticity. Other options like 'well-documented references' or 'detailed technical terms' are usually not characteristics of phishing since attackers want to confuse or bait victims with as little effort as possible, and spelling and grammar mistakes can be a sign but are not as definitive as the use of urgent language.