Why can some people roll their abdominal muscles?

Some people are able to roll their abdominal muscles, also known as voluntary rectus abdominis contraction (VRAC), due to the presence of multiple tendinous intersections within their rectus abdominis muscles. These tendinous intersections divide the muscle into segments, allowing for independent control of each segment. This ability is not present in everyone and is thought to be influenced by genetics and individual muscle anatomy.