Hydraulic backspin brakes

Grandma goes out to buy a car. The salesman says, I recommend this one. Grandma asks why. The salesman says, “Because it has hydraulic backspin brakes. Get in and I’ll show you.” He drives the car 100 miles an hour toward a brick wall, and when he’s 100 feet away he jams on the brakes. They stop a foot from the wall. The salesman says, “Do you smell that?” Grandma takes a sniff and says, “Uh-huh.” The salesman says proudly, “That’s hydraulic backspin brakes.” That night when grandpa gets home, grandma says, “Dear, I bought a car.” Grandpa asks, “How did you decide which kind to buy?” She says, “I bought one with hydraulic backspin brakes. Get in and I’ll show you. They get in, and she drives 100 miles an hour toward the same brick wall. When they are 100 feet away from it, she jams on the brakes, and they suddenly stop one foot from the wall. Grandma looks over at grandpa and says, “Do you smell that?” Grandpa says, “I ought to! I’m sitting in it.”