During the second trimester features like the eyebrows and fingernails start to grow. The umbilical cord continues to thicken as it carries oxygen and nutrients to the fetus at about week 16, the fetus’s eyes will become sensitive to light, and it will be able to make facial expressions like frowning and squinting. By week 18, the fetus has developed the ability to swallow and to hear a white paste covers the fetus’s body to protect it. The sucking reflex develops. If the hand floats to the mouth, the fetus may suck on their thumb. During weeks 20 to 24, a covering of fine hair develops all over the fetus’s body. The brain is developing and the eyes begin to open. The kidneys are functioning and begin to produce urine. The bone marrow begins to produce red blood cells at about week 21. By week 22, the taste buds are forming on the fetus’s tongue. The reproductive organs have developed the lungs, liver and pancreas continued to develop by the end of the second trimester, the fetus measures over 30 centimeters in length.