NEW YORK – A teenager posts a Twitter message saying he’s going to blow up a school. A husband grumbles that he’s looking for a hit man to kill his wife. A wannabe jihadist says in an Internet chat room that he is ready to become a martyr.

Are any of them serious? Or is it all bluster?

Separating real threats from idle talk is a workaday task for law enforcement. It is rarely easy, but it has taken on extreme complexity in the lurid case of Gilberto Valle, a New York City police officer charged with plotting to kidnap, cook and eat women he knew.