Julian's magician-mentor Gopal gives him a little monkey figurine along with a little moral lesson:
'Gopal gave me this little sculpture. It can do tricks.' Julian then stood the little figure first on one foot, then the other; one arm, then the other. 'You see, this monkey can balance on any one of its four limbs.' (4.19)
Get it? Four limbs, four Souls.
Well, in case you don't get it, Konigsburg spells it out for you. After she smacks down Hamilton Knapp for burping in class, the four of them perform this little number:
Suddenly Nadia Diamondstein thrust her left leg straight out into the aisle. Noah Gershom, who was three seats in back of her, stuck out his right leg. Ethan Potter saw and raised his right arm in the air. As if on cue, Julian Singh raised his left fist. For a moment above and below eye level, all four limbs stuck out, and then, just as quickly, all four disappeared. It was quite a balancing act. (6)
And it's just performed a pretty cool trick: giving Mrs. Olinski her groove back.