Using a piston to push a slimeblock horizontally removes the block below the slime block.

If one sets a piston horizontally and makes it push a slime block horizontally, the block beneath the extended piston's arm disappears.

The steps:
1) Place a sticky piston down and make sure it's pushing horizontally
2) Place a slime block in front of it.
3) Set the piston off with a redstone torch.
4) The block beneath the piston's extended arm has disappeared.