Check your grammar now! : intense or paroxysmal excitement; especially : the rapid pleasurable release of neuromuscular tensions at the height of sexual arousal that is usually accompanied by the ejaculation of semen in the male and by vaginal contractions in the female.
So, even though you may have only burned 250 calories during your HIIT workout, the total calories burned after will be far greater. Those calories, plus the 250 burned during the HIIT workout surpasses the 400 burned during the slow, steady-state workout by a LONG, LONG way.
The most I've burned from an Insanity workout is 621 calories from Max Interval Circuit, and I give it my all and my heartrate is always at 90% or more of my maximum. I'm 5'4 and weigh around 165 and have a FT7 Polar heartrate monitor.