There are two ways to hold the top of the acorn. One is to open had it, the other is to crimp.
Crimping on large surfaces just like the acorns cupscales, introduces little climber hands to advanced hand technique in a friendly environment. The cupscales ( texture near the stem ) has a lot of tiny bumps that a hand can find just the right way they want to grab it.
Upside down and on its sides, the shell offers several pinches. This is a challenging hold for children which is exactly why you should buy it.