Always looking for snappy ways to control brain cells, researchers have engineered mammalian and nematode neurons to wink off at the touch of a laser beam. The secret is engineering them to produce light-activated proteins that pump chloride ions outside of the cells, briefly desensitizing them. Using a previously developed laser "on" switch, the researchers caused nematode muscles to contract and relax by switching between blue and yellow laser light, they report in this week's Nature.