Possibly, you are thinking of Alternating Current?
Alternating Current. Usually made by an alternator (rotating electrical generator), but these days can be made by electronic 'Inverters'.
Alternating current
current
A fan
the wind moves the flag
sound
demonic possesions
if a part of the body moves back and forth
The fastest seismic wave that also moves back and forth is the P-wave.
A fan
the wind moves the flag
it moves its body back and forth
something moves back and forth
sound
demonic possesions
AC (alternative current) goes back and forth (the flow of the current changes periodically) DC (direct current) has a continuous flow
if a part of the body moves back and forth
That's because the water doesn't move, either. The water moves back and forth slightly, as a result of the wave; the wave energy moves on, WITHOUT taking the water with it. The wave is not a current.
then the egg will most likely being moving back and forth as well, especially if the chick is almost ready to be hatched
... Current surges back and forth.