No tricks. Just physicsΒ
Let's drop the ball (without initial velocity) on the floor from the height H.
It will bounce off the floor to a height h1 < H.
Let's drop another ball ...
It will bounce off the floor to a height h2 < H.
Now, what if you put the ball on the ball and drop them both (without initial velocity) on the floor from the height H ?
Let's take a look...
How can the ball bounce higher than the height from which it was dropped without initial velocity?