This video, created by Destin Sandlin of Smarter Every Day, showcases the collision of two vortex rings of dye in water. Sandlin recreated an experiment originally conducted by T. T. Lim and T. B. Nickels but with much higher visual fidelity. I think that the visual of the two different colors of dye colliding and forming new rings is quite striking, especially against the white background. I also appreciate the dedication of Sandlin to design and build a controlled setup to conduct this experiment. I also think that this is a fascinating phenomenon because it is still unknown exactly how the smaller, orthogonal rings form.
This video was posted to the Smarter Every Day Youtube Channel, created by Destin Sandlin.
Original Paper: Lim, T., Nickels, T. Instability and reconnection in the head-on collision of two vortex rings. Nature 357, 225–227 (1992). https://doi.org/10.1038/357225a0