If only Number Munchers had known when you were getting frustrated.

A new pilot computer program reveals how hard a kid finds math problems just by watching her face as she works, researchers report. In the future, a math game with built-in face-reading technology could adjust itself to individual kids' ability, the program's creators, a team of communications researchers from Tilburg University in the Netherlands, write in a new paper.

Google Scholar searches show that computer scientists have worked to make software that detects people's moods based on facial cues since at least 2002. I saw an MIT project at last year's SIGGRAPH conference, which captured live video of every conference attendee in the room and layered a virtual red, yellow or green cartoon face over everyone's body, depending on his mood. (It was as weird as it sounds.)