When Leonard and Amy play Where's Waldo, they remove their glasses and squint. Given myopia (nearsightedness) is far more common than hyperopia (farsightedness) among young adults in North America, we can assume at least one (more likely both of them) wears glasses for distant vision. In this case, removing their glasses would improve their ability see up close and find Waldo while reducing their need to squint.
During the pie eating contest, as Amy starts counting down a second time (after Sheldon's interruption about anti-oxidants), just after she says "two", Penny takes a quick peek at the camera.
When Sheldon draws the solar system, he mistakenly puts three items in the same orbital path.