https://newatlas.com/science/neanderthals-glue-tools/sample quote
In order to successfully use the bitumen, the researchers also discovered that the creators of the implements had to mix it with ocher, a natural pigment. The exact mix of ocher to bitumen, which they found by whipping up their own bitumen/ocher concoctions, would be just right for making handles that could stick to shards of stone, but not to human hands. In other words, they were perfect handles. Arriving at this mixture and applying it to tools, say the researchers, points out a high level of cognitive reasoning in Neanderthal species.
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