Someone cuts you in line for coffee, and you feel the redness coming on. You tell yourself you're not really that angry, but by now your face looks like a tomato. It’s curious that the same thing happens when you're embarrassed or nervous, which seem like they’d be on the other end of the emotional spectrum. But as this video from SciShow explains, you're reacting to an immediate stress in all three instances. And your response is totally involuntary: Your pupils get bigger, your heart beats faster, and your blood vessels widen so you can get more blood to your muscles for fight or flight (thanks, ancestors!). And lucky for you, the blood vessels in your face are close to the surface, so when they dilate, your cheeks get that pinkish hue.