You can control an iPhone or iPad with your mind – well, really just your head. Apple's accessibility features includes head-gesture controls.
Thanks to the device's camera, your tablet or phone can tell when people shake their heads to the left or right. These visual cues can control tapping, switching apps, notification center, Siri, changing the volume, and several other features.
Turn on this setting by going to Settings, General, Accessibility, and Switch Control.