During pregnancy, these painless tightenings are called Braxton Hicks contractions. When you are having regular, painful contractions that feel stronger and last more than 30 seconds, labour may have started. As labour gets going, your contractions tend to become longer, stronger and more frequent. During a contraction, the muscles in your womb contract and the pain increases.
During initial stages of assimilation, Borg nanoprobes began attaching themselves to the victim's red blood cells, allowing them to circulate throughout the body. (VOY :  Scorpion ) Within minutes, the nanoprobes spread visibly through the capillaries of the victim's skin.
In the human digestive system, the process of digestion has many stages, the first of which starts in the mouth (oral cavity). Digestion involves the breakdown of food into smaller and smaller components which can be absorbed and assimilated into the body.