The sad faces of the common people that he included in many of his paintings.

The choice of bright colors.
The swirling circular shapes left on the canvas by his brush.

Nick's answer is very good regarding the painting technique. The book has the exact same name as in your question it was written by Richard Muhlberger.

Having been painted by Van Gogh is what makes a Van Gogh a Van Gogh.

You ask what makes a van Gogh? Well,... I'll tell you exactly,... straight forwards and straight up front. In order to make a van Gogh, first you must be gassed up, I'm guessing like burping fumes from the liquid called the Green Fairy. This will work just like it does with the rails that run down the quarter mile.

This is called super fast speed my friends, Just as Vincent was known to paint,.... sometimes, or should I say most times, five to eight large canvases a day, just like he was known to tell his own art dealing brother in the letters written to him by Vincent.

In some of his known meticulous works of supposed art and of all the ones you can see the time that it would have taken the artist in the completing of them, of all the dried and overlaid build-up of paint, you just might want to come to the rightful conclusion that you are just looking at a copied piece of his work done in his supposed style by a copyist that forgot to get gassed up.

Van Gogh had a specific way of applying the paint in thick, often wavy layers of paint that became his signature style. It is also reflected in the beautiful drawings he made in ink, with a raw feather nib.