An atomic nucleus usually has a well-defined shape — elongated like a melon or flattened like a pumpkin. But silicon-30 behaves differently: it seems unable to make up its mind.
Entangled photons are like two couriers marching in lockstep: their quantum states, particularly polarization, are synchronized so that measuring one instantly determines the state of the other, even at a distance. In a material, this synchronization gets disrupted.