WHEN you get behind the wheel of a car and are offered the choice of driving either in Sport mode or - would you believe it - "Insane" mode you know you are sitting in something completely different.
And the Tesla Model S is certainly different.
It's the electric car which has the kind of blistering performance that can upset any self-respecting Aston Martin or even Ferrari owner.
It may be powered by batteries but when it comes to acceleration it's truly in the supercar league.
Strangely enough my first few miles in the driving seat of a Tesla Model S P85D lulled me into a false sense of sedate, relaxed motoring.
The large, luxury saloon which is built in America's Silicon Valley purred along in almost total silence just like any other electric car I have driven.
Trying to get to grips with a car on which everything is controlled by a giant 17-inch touch screen - there are only two buttons on the entire dashboard, one for the glove box and the other for the hazard lights - concentrates the mind somewhat.
But having worked out the essentials I found myself on an open dual carriageway and pressed the accelerator hard, only to find the cars behind me seemed to have gone into warp speed reverse.
I've driven quicker cars - but not many. And none of them delivered the sort of power the Tesla does in complete silence.
Hitting 60 miles per hour in just 4.4 seconds the Tesla's power from twin electric motors is awesome. And I was only in Sport. Insane mode was still to come.
But the Tesla Model S is not just about power. It's a high-tech automotive wonder which will - via an app on your phone - drive itself out of your garage.
When you return home the car will also take itself back into the garage.
The latest models come with Autopilot, which when switched on not only keeps the car safely in the lane you are travelling in but also - when you signal to pull out on the motorway - automatically and safely moves you into the next lane while keeping you well away from other traffic. Clever, but something you definitely have to get used to.
It hasn't quite reached the stage where the driver feels redundant but it's getting close.
This all-wheel-drive smart car also knows that, without an engine, you are reliant on charging points so if you set the sat nav for a particular destination and it feels you don't have enough reserve power to reach it you will automatically get a route which takes you via a charging point.
There are numerous public charging points around the country but in addition to them there are now Tesla Superchargers at 31 locations in the UK which will give the car a 180-mile charge in just 30 minutes and are free to use. Most people, however, would normally charge their cars up at home overnight.
On full charge a P85D will run for anything up to around 300 miles, although the wider range P90D can cover around 340 miles. And the company claims that for every £3,359 you would spend on petrol to run a similar sized car it will cost you £567 in electricity to run a P85D.
Inside the cabin the five-seater Tesla boasts full leather upholstery with Alcantara on the top of the dashboard and roof lining.
There's a double panoramic glass sunroof, the forward section of which retracts when you drag your finder backwards over the picture of the car's roof on the touch screen, simulating an opening movement.
In fact this car is packed with forward thinking and in some cases gimmicky ideas. When you use the indicators, for example, the indicators on the car pictured on the touch screen start flashing too. And the exterior door handles retract into the bodywork when the car locks itself as you walk away and pop out again as you approach the car.
But at the end of the day the most impressive aspect of the car - apart from its silence - is its dynamic acceleration.
And so to the aptly named Insane Mode. Switch to this and the 0-60mph time is slashed from 4.4 seconds to an awesome and 3.2 seconds. It's as if you have been lifted up and carried forward on a silent whirlwind.
While other supercars are all exhaust roar and gear changes the Tesla does it all in a silent whoosh in a single gear, normally terrifying unsuspecting passengers and leading to a few expletives.