[squarefoot]

Those walnuts look suspiciously as they were already weakened. There's a way to open walnuts without breaking them by gently inserting a knife with round tip in the weak point where the two shells join on the upper side then rotating it, and it looks like they used the trick to weaken at least a couple walnuts in that bowl.

[Perz1val]

They do look suspicious, but I've crushed walnuts that actually are that weak (and really light). I think it is a combination of storing conditions and variety.