Complex sentence: Rectilinear locomotion or rectilinear progression is a mode of locomotion most often associated with snakes, particularly heavy-bodied species like terrestrial pythons and boas, although most snakes are capable of it.
Split into simpler sentences: 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 pythons and boas, although most snakes are capable of it.