When you place a block right when any entity enters it, the block will disappear and the item in your inventory will be consumed.

How to reproduce

1. Summon any mob (Creeper or Zombie are the easiest)
2. To make it easier, switch to survival mode, and the mob will chase you.
3. Place any block right in front of the entity
4. (x)The block disappears because the entity is on the same block. The item in your inventory is also consumed.

 | What happened in the images?
V That creeper removed my slime blocks (I did it 2 times (hard to show with images))