Yiddish: He has more brains in his little finger than others have in their heads.

SOURCE: Stutchkoff, Der Oytser fun der Yidisher Shprakh.  Variations:

... more brains in his left foot ... | ... mer seykhl in linkn fus ... | ... מער שׂכל אין לינקן פֿוס ...

... more brains in his heel ... | ... mer seykhl in pyate ... | ... מער שׂכל אין פּיאַטע ...

SOURCE for all:  Stutchkoff, Der Oytser fun der Yidisher Shprakh

ער האָט מער שׂכל אין קליינעם פֿינגער ווי אַן אַנדערער אין קאָפּ.

Er hot mer seykhl in kleynem finger vi an anderer in kop.

He has more brains in his little finger than others have in their heads.