An injector, for injecting fluid from a cylinder inside an animal target, includes a drive ram, movable along its longitudinal axis bidirectionarily in a first ram direction and a second ram direction; a motor, coupled onto the drive ram to selectively make the drive ram go forward and retract along the longitudinal axis; and a trigger, which is moveable, capable of biasing on the first and second trigger directions, and produce control signals for the motor, whereby the drive ram moves along the longitudinal axis in the first ram direction when the trigger moves on the first trigger direction, wherein the trigger control signal is transmitted from the trigger onto the motor in wireless.