Three seconds before the preview runs out, the player says so and the gold drains out of the waveform; when the music stops, the unlock pill lights up and the padlock stays ajar.
The unlock pill is visible and filled from the first second, so nothing about buying arrives as a surprise at the end.
With Reduce Motion switched on, the colours still change and the movement does not, and the moment reads in full on a phone that asks for less animation.