like what was previously said having badly distributed weight on the trailer can make it sway....to much on the toungue (front) cand make it want to push ur rear end around. too much to the back can make it try and lift the rear of the car off the ground which i think is what the problem was in this vid.

#1....you shouldnt tow a car with a car

#2...you shouldnt tow a heavy car with a car

#3...that cars towing capacity would be nothing near the weight it was pulling

#4...once the trailer started swaying, the driver didnt seem to do anything right away to compensate ie. lift off the gas (might not have helped) or slowly get back into it to try and pull it out of the weaving.

#5...driver left his brain at home

you do not lift off the gas if you have trailer sway. you GIVE it gas to get rid of trailer sway.

trailer sway can happen even if you have perfect weight distribution, but bad distribution does make it happen faster.

i've had some light trailer sway caused by wind upset when getting passed by a semi.

Yup, even just the ruts in the road can cause it. You have to pull the trailer out of the sway then slow down once it's straightened out.