@DAMIADENUGA The water remains a supercooled liquid.
When you take the bottle out and shake it, tap it or even open it, that small disturbance provides a starting point for ice crystals to form.
The water then appears to freeze almost instantly, often within seconds
@DAMIADENUGA It is called Supercooling
Normally, water freezes at 0°C (32°F).
However, if very pure water is left undisturbed in a freezer, it can cool to below 0°C without actually forming ice. This is because there are no impurities or disturbances to trigger ice crystal formation.