1️⃣ Model: Add Cylinder → delete top face → extrude neck. Duplicate, scale inside = liquid.

2️⃣ Cut line: Add Cube (flat “slice”). On liquid: Boolean – Difference (Object: Cube). Parent liquid to bottle (Ctrl+P).

3️⃣ Keep level: Add Empty, parent to bottle. On Cube: Constraint – Copy Location (Target: Empty, Z only, Offset on). Rotate bottle — the Cube’s Z stays level.

4️⃣ Ripples: Subdivide Cube. Physics on Cube: Dynamic Paint – Canvas (Waves). On bottle: Dynamic Paint – Brush. Press Play and rotate — waves drive the cut surface.

5️⃣ Look: Bottle = Glass (IOR 1.50) + Solidify for thickness. Liquid = Glass (IOR 1.33) with a tiny blue tint. HDRI + one rim Area Light. Add DOF.

6️⃣ Animate: F1 keyframe, F60 rotate, F120 opposite, loop.

👉 Fixes:

Glitches? Apply Scale, try Boolean “Fast,” add loop cuts or a Remesh (before Boolean).
Waves too soft? Higher Speed or more subdivs.
Liquid clipping? Keep it close to, not touching, the glass.

Enjoy and make a splash! 💦