Using the Slide-In and Slide-Out interactions, and changing the Mask original size, I upgraded each slides behaviour to grow and shrink.
You can clone this project and copy the slider for any use...
When your bath soap bar gets too small to use, don't throw it away! open the next bar, and when you finish showering, stick the small old bar to the back of the new bar. Onces they both dry, they will become one.