When you first glance at artist João A. Carvalho's notepad paper illustrations, you may think you're seeing 3-dimensional objects. But on closer inspection, they're actually simple but clever illusions that use lines and shading to make images pop from the page.
Of course, Carvalho isn't drawing his pieces on pre-lined paper. Instead, he's using the appearance of lined paper to enhance his illusions. You can see more of Carvalho's work, both illusory and non, on his Facebook page.