This ones hard-how did carol know?

Question

Carol is traveling by ship from south of the equator to the north.

She has a nice little second class cabin which has a bathroom, but no window.

Carol has no compass nor other instruments.

Yet, without leaving her room or talking with anyone, Carol knew exactly when the ship crossed the equator.

How did she know?

Answer 1

The water in Carols toilet would spin clockwise when flushed when the ship was south of the equator and spin counter-clockwise when flushed when the ship was north of the equator.

Answer 2

She ran the tap and the water swirled in the opposite direction...?

Answer 3

she done flushed the toilet and saw it swirl counterclockwise