Piston Blocks and sucks up Blocks

I was playing around with Redstone Clocks, so I found out this.
It's hard to descibe so I made an Video:
http://www.youtube.com/watch?v=4o9NI3YB6zA&feature=youtu.be
But im trying.
When a Piston is added to an Clock, and another Block will be pushed in front of it, it will suck up the Block or stops the Clock.