Echo / bounce

The mechanic

Because these letters are both plosive and voiced, releasing them while they carry sukun produces a small audible bounce. Five letters, gathered as قُطْبُ جَدٍّ: ق ط ب ج د.

Where it occurs

The five qalqala letters, when they carry sukun

ق ط ب ج د

A place in the text

لَمۡ يَلِدۡ وَلَمۡ يُولَدۡ

The marked spot was located in this ayah's own text at build time — Al-Ikhlas 112:3.