Snare injuries to chimps are reported at many sites across east and west Africa where chimps are studied, with many animals dying in the traps.
However, very few snares injuries have been reported among chimps studied at Bossou, which is unusual as the chimps live close to human settlements and snares are commonly laid in the area.
Now primatologists know why.
While researching the chimps, Mr Ohashi and Prof Matsuzawa, of the Primate Research Institute at Kyoto University, Japan, observed five male chimps, both juvenile and adult, attempting to break and deactivate snares.
On two occasions witnessed, the chimps successfully deactivated the traps set for them.
A typical snare, for example one made by the Manon people of Bossou, consists of a loop of iron wire connected by a vine rope to an arched stick, often a sapling.
On six separate occasions, chimps attempted to deactivate the traps
The sapling puts tension into the rope and once an animal passes through the wire loop, the trap is sprung and the sapling pulls it tight, around the neck or leg of an animal.
Such traps cause indiscriminate damage, ensnaring any and all animals that come into contact with them.
But male Bossou chimps have worked out how to outwit the hunters and deactivate the traps.
"They seemed to know which parts of the snares are dangerous and which are not," Mr Ohashi told the BBC.
A rat caught in a snare is found by researchers
In the journal Primates, the researchers describe six separate cases where chimps were observed trying to deactivate snares.
Mostly, the chimps grasped the snare stick with their hands, shaking it violently until the trap broke.
Sometimes a chimp lightly knocked the sapling that holds the snare, before grasping it to break the trap.
But in all cases, they avoided touching the dangerous part, the wire loop.
In the video above, chimp can be seen seeking out and inspecting snares, without breaking them.
"We were surprised when we found this behaviour," says Mr Ohashi.
"This is the first report of chimpanzees breaking snares without injury."
The chimps' actions may also reveal something important about how chimps learn.
Often, chimps acquire new talents by trial and error.
For example, when trying to crack nuts, they might strike one stone onto an anvil stone and miss the nuts all together. Or they might use their hands to strike the nut, which is ineffective.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.