Which type of snake uses both serpentine and concertina forms of movement? A. python
B. rat
C. boa
D. grass

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.

"the sandy walls seemed to collapse in on themselves"

and

"the bloodshot waters seemed to have no bottom"