A ground is a connection between an electrical circuit and the Earth.

Electricity naturally flows to the planet ("flows to ground") through anything that can conduct electrical current, and it is continually seeking such a path. The conductivity of concrete is enough to provide a path for deadly current when there is sufficient voltage available.

Living creatures conduct electricity: there are charged potassium currents in your body (in the 10-millivolt range). Nerve cells communicate to each other by acting as "transducers," creating electrical signals (very small voltages and currents) in response to the input of certain chemical compounds called neurotransmitters.

Nerve cells release neurotransmitters when stimulated by electrical signals. (The effect of amiridin and tacrine on the potassium currents in a nerve fiber. IuV Burov, EM Peganov, and LM Shapovalova. Biull Eksp Biol Med, October 1, 1993; 116(10): 397-400.)