Water
WATER has a wave, stillness and flow In & out( up down) quality and Reflects;
Most of Earth and beings are made up of Water.
The heart, brain and pulse frequencies of Sentient beings is much like Water -flow ( in out, up down Frequencies), introspects & realises ( stillness) and Reflects one's intents ( mirror Neurons in brain).
The use of Water by Scientific practioners in Meditation, in Vedic and later in Zen meditation is quite prevalent ;
Neuro Chemicals and fluids gain a Calmness with correct Tuning of Water flow around