How does glass 'shake' and why does it start flowing when pushed hard enough?

Glassy materials are everywhere, with applications far exceeding windowpanes and drinking glasses. They range from bioactive glasses for bone repair and amorphous pharmaceuticals that boost drug solubility to ultra-pure silica optics used in gravitational-wave detectors. In principle, any substance can become glass if its hot liquid is cooled fast enough to avoid forming an ordered crystal.