The Asian elephants (Elephas maximus) involved in the study had already been taught that pulling on a rope brought a platform towards them, and a food reward on that platform within reach.
But this apparatus, set up at the Thai Elephant Conservation Center in Lampang province, presented them with a new twist on that simple task.
One rope was threaded all the way around a platform – like a belt through belt loops – so if one end was tugged, the rope simply slipped out and the platform did not budge.
But if two elephants each took an end of the rope and pulled, the platform moved and that could claim their treats.
"When we released one elephant before the other, they quickly learned to wait for their partner before they pulled the rope," Dr Plotnik told BBC News.
And one elephant – the youngest in the study – quickly learned that it did not have to do any pulling to get a treat."They learnt that rule [to wait for the other elephant to arrive quicker than chimps doing the same task.
"She could just put her foot on the rope, so her partner had to do all the work," said Dr Plotnik.