The video is fascinating (although you may want to hover your finger over the mute button while telling the narrator to STFU). A plant rocks back and forth like a metronome, while nearby vegetation remains (relatively) still. After the swaying is manually stopped, the plant resumes its oscillation.
This is of particular interest to me, because my wife and I have observed the identical phenomenon happening with one particular plant on a hillside within view of a back window at our home. When we first spotted it we watched with binoculars, expecting to see critters of some type disturbing the plant. We even wondered about underground activity, but that made no sense.
The limited web-based research I've done seems to indicate that what is depicted is a plant's resonant frequency being magnified by imperceptible air currents. I found one study in the American Journal of Botany:
Free oscillations of upright plant stems, or in technical terms, slender tapered rods with one end free, can be described by considering the equilibrium between bending moments in the form of a differential equation with appropriate boundary conditions. For stems with apical loads, where the mass of the stem is negligible, Mathematica 4.0 returns solutions for tapering modes α = 0, 0.5, and 1. For other values of α, including cases where the modulus of elasticity varies over the length of the stem, approximations leading to an upper and a lower estimate of the frequency of oscillation can be derived.It looks like magic, or a paranormal phenomenon, or a hoax, but what it boils down to is -
Video via Nothing to do with Arbroath.