In order to sneak into the museum, Henry needs to pass a guard on the rooftop. He can do this by taking the invisibility pill, which turns him invisible. However, the effect backfires as Henry also loses the ability to see, and doesn't know where the entrance is, so he falls off the roof and this leads to a fail.
- While it can be confusing why Henry couldn't see after becoming invisible, this is explained by science. For something to be invisible, light has to pass through that object and not reflect off it. This involves all parts of Henry's body, including his eyes. Technically, no part of the eye can work without light refraction, which doesn't happen if the light passes through the whole eye.