He started to question his entire life - Listen for the hissing scratch in the tempered glass

Yeah... it should not be on there at all. AND when he pushed it, there was either a jagged bit of pottery or quartz in the pottery, or some quartz grit between the pot and the table, that caused that NICE LOUD scratch deep into the surface of the tempered glass. That glass is pre-stressed, by the formulation of the glass, and very fine heat treatment, by running lots of tiny and very hot flames across the surface, so the glass heats and then shrinks, creating a very fine criss crossing pattern of tension in the glass, from the shrunken surface layers, which makes the glass smaller on the outside, than the inside - as soon as there is a crack propagation point, the glass essentially just explodes into small granules. That scratch created the trigger point. This is the point of safety glass - when people stupidly stand on glass table tops, or fall through glass shower screens, or have car crashes, they are no longer having horrendous injuries from huge chunks of razor sharp glass going through them...

https://en.wikipedia.org/wiki/Tempered_glass -----------