Why does it soon turn red when tightening a finger?

1) The constriction causes stagnation of venous blood, veins swell, capillaries expand. 2) Fresh arterial blood does not flow, and venous blood becomes dark, the finger turns red.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.