Epinephrine

A close-up of a human eye in black and white, with the iris contracting and dilating in a rhythmic, pulsing motion. The eye blinks slowly, the eyelid closing and reopening, while the pupil shifts slightly in response to changing light. The surrounding skin and eyelashes are visible, with fine details of the sclera and blood vessels. The sequence loops, showing the eye opening wide, then contracting, and repeating the cycle.