Saif Mohammad and colleagues from the National Research Council Canada, used sentiment analysis to uncover the feelings buried inside email. "It's an efficient way of generating data about the emotional content of huge amounts of text," says Mohammad. "There's been a lot of research based on positive and negative emotion, but with all this data available it makes sense to understand what we can learn from all the emotions."

The team created a huge "sentiment" database using crowdsourcing by hiring workers for Amazon's Mechanical Turk to pair 24,200 words with emotions – "ice cream" paired with "joy", for instance, and "gardening" with "peace".