A glass rectangular block if seen through the side edge can make a pencil seem broken.
Why does the pencil look broken? From above we can work out what is happening. The light ray from the pencil passes from a fast to slow medium and turns towards the normal line (remember FAST SOFA).
Picture looking from above.
The light ray passing through the glass block passes from a slow medium to a fast medium and moves away from the normal line (again remember FAST SOFA).
If you look at an animal from the side of a tank that is half in the water half out of the water it can look split. This is refraction in action.