"They learnt that rule [to wait for the other elephant to arrive] quicker than chimps doing the same task.
And one elephant - the youngest in the study - quickly learned that it did not have to do any pulling to get a treat.
"She could just put her foot on the rope, so her partner had to do all the work," said Dr Plotnik.
Many scientists, photographers and film-makers have documented remarkable behaviour by wild elephants, including "targeted helping" of other elephants that become stuck in mud.
There have even been reports of elephants appearing to mourn their dead.
"As humans, we like to show that we're unique," said Dr Plotnik, "but we're repeatedly shot down.
"One thing that remains is our language. But amazingly complex behaviours - culture, tool use, social interaction - we see all of this in the animal kingdom."
Dr Karen McComb from the University of Sussex, who studies animal behaviour, agreed that the study enhanced "our understanding of the cognitive abilities of this intensely social animal".
Dr Plotnik also hopes that his findings will help with the conservation of these endangered animals.
"The more we can understand about their intelligence, the better we can develop solutions to things like human-elephant conflict," he explained.
"So when the animals are raiding crops, we need to think of solutions that are based on the reasons why, and that benefit elephants as well as people."
Tina Dow from US-based Elephant Research International said the findings could also "have positive effects on captive elephants, allowing keepers and mahouts to develop better enrichment tools that can stimulate both mental and physical health".
"Elephants are caring, sentient beings," she added.
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