Got it.
On the back edge of the horizontal plank, the operator has attached 2 metal rods (one on the left and one on the right side) that can swing down. Since the plank is placed slightly over the edge of the table, they can connect past the back of the table to a rocking mechanism that is hidden under the table.
See how careful the opertaor holds and then places the plank after the cut (0:24 - 0:28). Watch the synchronized motion of his 2 ringfingers to rotate the rods down (0:27). The gentle rocking that follows (while he grabs the balls) is what happens when the 2 rods connect to the mechanism. Strange how that entire thing balances, rocks, twitches and then settles in an equilibrium… (0:29 - 0:33).
Final proof: once the contraption tilts, you can clearly see the reflection of the rods under the plank on the lifted side (about 5cm from either end). These reflections are absent before he put the plank down. Compare 0:24 with 0:35 & 0:39. These reflections were also not present before the cut: compare 0:10 with 0:35.
