Bending light

How would you explain this phenomenon?

And this one?

 

Polish team managed to explain this phenomenon in the following way :

 

There are our questions for you:

1. How to explain this ?

2. An appearing coin.

We are stepping back from the coin that is placed on the bottom of the cup until it disappears completely and be hidden behind the cup’s wall. After filling the cup with water, the coin is visible again. Do you know why?

POLISH VERSION

3. Not all shadows are black.Why?

Speed of light