A comprehensive quantum chemistry study with natural bond orbital analysis is performed to reveal the intrinsic properties of the floppy potential energy surface of the smallest methonium ion CH5+. In contrast to the low-energy barriers of C-s(I) -> C-s(II) -> C-s(I) and C-s(I) -> C-2v -> C-s(I) that correspond to the H-2 rotation and H-flip motions, the remarkably larger intramolecular interaction energies are the driving power to mimic the hydrogen scrambling in CH5+. As for the H-2 rotation and H-flip motions, the hyperconjugative and electrostatic interactions compete strongly. They together with other interactions compensate for each other and lead to the floppy potential energy surface.