The conventional antipsychotic drugs have a problematic side effect involving abnormal movement. this side effect is called

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.