Unanswered to me at least. I have read many articles, forum discussions on quantum entanglement but never found anyone discussing these questions. Here they are: 1) How do they create (mechanism) entanglement? or How 2 particles are generated entangled? 2) What are the differences (properties) between 2 entangled and 2 non-entangled particles? Can we tell by looking at 2 particles if they are entangled or not without the 'entanglement test'? 3) What are the 2 heaviest entangled particles generated so far? Electrons, Protons? Neutrons? Is there any limit on mass for entanglement? 4) Is it true if polarization of one of 2 entangled photons is changed before detection, the other photon will also change its polarization? I'm really interested to know what makes 2 particles entangled. I think the answers to our entanglement problems lie in the process of entangling them.