Testosterone-fuelled people seem to enjoy provoking anger in others. At least,that's the conclusion of a study looking at people's responses to angry faces and their levels of testosterone. Michelle Wirth and Oliver Schultheiss at the University of Michigan at Ann Arbor measured the testosterone levels of 70 young adults and then gave them a learning task involving tapping out a pattern of keystrokes on a computer. After each repetition of the task they were shown a face with either an angry or a neutral expression, which flashed onto the screen for a few milliseconds-far too briefly to register consciously. The researchers found volunteers with high testosterone levels learned the keystroke pattern more quickly if they saw an angry face than other wise. Those with lower levels showed no such difference.