Fishtailing happens to a car when it swings back and forth uncontrollably. It is kinda like when you swing on a swing and you start to swing too high and your legs kick out to the sides. It is not safe to fishtail in a car because it can make the driver lose control and crash. It happens when the back wheels of the car lose traction on the road and start to slide. The driver needs to turn the wheel in the opposite direction of the slide to try to get the car back under control. It's important to drive slowly and carefully on slippery roads to avoid fishtailing.