[rodneym]

Bob and Tommy got it.
It's not that your rears locked but the speed differential between your tires and what your un-throttled drivetrain wants to do, will cause a braking effect, throwing the weight of car to one corner, and that's where you lost it.
If you haven't done a traction circle in your Cobra, you're missing alot. Keeping the balance of the car is paramount.
It's true for any car but the Cobra will accentuate these issues. They're great cars to learn on. Driving other sports cars will be much easier.
Speeds are faster nowadays but the skill was greater in the 60's.