It's the thick-walled muscular pouch that grinds food in a bird's lower stomach
[DOC] [TLE] gizzard - definition and meaning - Wordnik [PAR] n. thick-walled muscular pouch below the crop in many birds and reptiles for ... 
my stomach is called a gizzard and its duty is to grind and crush my food so that it
... [DOC] [TLE] gizzard - definition, etymology and usage, examples and related words [PAR] Pronunciation of gizzard and it's etymology.