When a block in a cobblestone generator is mined and one is subsequently instantly generated, it dosen’t show the breaking aniamtion on that block.
It shows the breaking animation just like any other normal block should.
1. Create a cobblestone generator.
2. Start to mine the cobblestone and do not let go of mining it. (I have found this is best done with a stone pickaxe. After a few blocks it should sync to the rhythm of the generator and you should eventually see this glitch occur. If it dosen’t, just stop and start again.)
3. Have a cobblestone instsntly generate when broken and continue to mine it.
4. Observe that that block does not show the breaking animation.