hand, face, crown (wristwatch), back
Grandfather clocks have "toe" molding around the base.
The clock stops when any part of your shoulders, chest or torso crosses the line. Head, arms and legs do not stop the clock.
Internal or biological clock
A clock has a neck and hands but no legs. The "neck" refers to the part of the clock that connects the face to the body, while the "hands" indicate the time. Despite these features, a clock does not have legs, making it a fitting answer to the riddle.
The biological clock that regulates the body's daily rhythms is called the circadian rhythm. It is controlled by a cluster of cells in the brain called the suprachiasmatic nucleus, which responds to light and dark signals to help synchronize our internal body clock with the external day-night cycle. This internal clock helps regulate functions such as sleep-wake cycles, hormone release, body temperature, and metabolism.
A person's body clock is the system of needs that your body takes. Your body will want to sleep during certain hours for example.
Internal or biological clock
The part of the brain that regulates the pacemaker is the hypothalamus, specifically the suprachiasmatic nucleus (SCN). The SCN serves as the body's primary circadian clock, controlling rhythms such as sleep-wake cycles and influencing the timing of various physiological processes. It receives input from light cues, which help synchronize the body's internal clock with the external environment.
The clock light is an integral part of the clock and is not replacable by itself
The pendulum is the part of a grandfather clock that swings back and forth. It regulates the timekeeping mechanism of the clock by controlling the rate at which the gears turn.
A part of a clock that starts with "pen" is the pendulum. The pendulum helps regulate the timekeeping of certain types of clocks by controlling the speed at which the clock's gears move.
A clock or a watch. They both have faces and hands, but no legs.
Pineal body (gland)