If it were that easy to tell whether someone was a sociopath I wouldn't be working on a degree in Forensic Psychology.
That video was a very common mental trick, most people would pick that color and tool if they were given that test.
Let me show you:
Ok, think of two shapes, not a square because that's too easy. close your eyes and picture them both clearly - now, put the first shape inside of the second shape.
See? A parlour trick.
There are a bunch of very similar tricks, some work better than others - most of them use the power of suggestion; there are a few posters here that are skilled in hypnosis and NLP that could explain it better than I.
Now there are a few good and simple tests that sociopaths and psychopaths do particularly poor at, such as the stroop test: http://en.wikipedia.org/wiki/Stroop_effect
But the only real way to identify a psychopath is by their actions and past behaviours. For instance, if your childhood friend who liked to dissect small animals grows up to end up being a deadbeat who spends most of his adult life in prison; chances are he's a sociopath. Although that's not usually the case with some people with the condition.