Human swimming typically consists of repeating a specific body motion or swimming stroke to propel the body forward. There are many kinds of strokes, each defining a different swimming style or crawl.
In high school, collegiate, and Olympic swimming, there are two undulating strokes (breaststroke and butterfly stroke) and two alternating strokes (front crawl and backstroke).
Rectilinear locomotion or rectilinear progression is a mode of locomotion most often associated with snakes. In particular, it is associated with heavy-bodied species such as terrestrial African adders, pythons and boas; however, most snakes are capable of it. It is one of at least five forms of locomotion used by snakes, the others being lateral undulation, sidewinding, concertina movement, and slide-pushing. Unlike all other modes of snake locomotion, which include the snake bending its body, the snake flexes its body only when turning in rectilinear locomotion.