When taking a pulse, the thumb should not be used because it has its own pulse, which can interfere with the accurate assessment of another person's heart rate. The presence of this pulse can lead to confusion and erroneous readings, as the sensation of the thumb's pulse may mask the pulse of the patient or subject being assessed. Utilizing the thumb can therefore compromise the reliability of the pulse measurement.
In contrast, the other fingers, such as the index, middle, and pinky, do not have their own prominent pulse and can effectively serve as tools for palpating the pulse of another individual. Each of these fingers has its unique characteristics, but they do not present the same complications in obtaining an accurate pulse measurement as the thumb does.