Under cooling, a supercooled liquid undergoes a glass transition and stops flowing. Physicists do not agree on the microscopic reasons that make a glass solid. Some view this phenomenon as being collective in nature: it may be a signature of a thermodynamic phase transition, or  being caused by kinetic constraints (where particles seek to solve a sort of Chinese puzzle). Others view it as simply reflecting elementary barriers for rearrangements, controlled by the elasticity of the material. Here I will introduce a novel algorithm to systematically extract elementary rearrangements in a broad energy range. It allows us to verify a quantitative prediction on the relaxation time, assuming that relaxation is not collective in nature. I will also propose a  theory of dynamical correlations in liquids based on coupled local rearrangements,  which connects this phenomenon  to avalanche-type responses observed in driven disordered materials. I will discuss connections between this view and recent measurement of sound emission in the creep response of  crumpled papers.