All of us who remember our science books from back in the day would agree that there really were some very creepy diagrams in these books. These diagrams would scare the little us, as we used to look at them. This guy here was reading an eBook version of a Science book, when he came across this really interesting diagram on his screen.
This showed a skeleton with another very creepy looking skeleton at the back. The guy surely was in no mood to study, which is why he suddenly noticed the creepy part in it. However, he wasn't willing to let the opportunity for a joke slide by, which is why he posted a funny picture with the skeleton at the front asking a funny question about what was standing behind him in the book.