> And they sure are effective—it’s very difficult to walk by a billboard that appears to be popping out of the wall without being captivated by it. This isn't

> And they sure are effective—it’s very difficult to walk by a billboard that appears to be popping out of the wall without being captivated by it. This isn't really how they work, in my experience. In reality, people on the street who are interested in seeing the billboard attempt to gather at a single vantage point where the illusion works. If you stand anywhere else on the sidewalk, the image becomes distorted, and the illusion breaks. My guess is that the trucks in question exploit the fact that when I'm driving behind one of them, I'm stuck at that single vantage point where the illusion works.