Should the stooper guess correctly, they all change places, and the jumper forms the back.
The boy who in jumping knocks off either of the things has to take the place of the stooper.
"bend forward," Old English stupian "to bow, bend" (cognate with Middle Dutch stupen "to bow, bend"), from Proto-Germanic *stup-, from PIE *(s)teu- (see steep (adj.)). Figurative sense of "condescend" is from 1570s. Sense of "swoop" is first recorded 1570s in falconry.
"raised open platform at the door of a house," 1755, American and Canadian, from Dutch stoep "flight of steps, doorstep, stoop," from Middle Dutch, from Proto-Germanic *stopo "step" (see step).
[1930+ Underworld; fr earlier sense ''decoy,'' fr the early 1800s practice of fastening pigeons and other birds to stools or stands as decoys; this term was applied to the decoy or ''hustler'' for a faro bank]
(also stoolie) A police informer; stool pigeon: He's nothing but a cop's stool (Underworld 1906+, variant 1924+)
: to make me stool on a friend (1911+)
[back formation fr stool pigeon]