'To fret the gizzard' definitions:

Definition of 'To fret the gizzard'

From: GCIDE

Gizzard \Giz"zard\, n. [F. g['e]sier, L. gigeria, pl., the cooked entrails of poultry. Cf. Gigerium.] [1913 Webster]
1. (Anat.) The second, or true, muscular stomach of birds, in which the food is crushed and ground, after being softened in the glandular stomach (crop), or lower part of the esophagus; the gigerium. [1913 Webster]
2. (Zool.) (a) A thick muscular stomach found in many invertebrate animals. (b) A stomach armed with chitinous or shelly plates or teeth, as in certain insects and mollusks. [1913 Webster]
Gizzard shad (Zool.), an American herring ({Dorosoma cepedianum}) resembling the shad, but of little value.
To fret the gizzard, to harass; to vex one's self; to worry. [Low] --Hudibras.
To stick in one's gizzard, to be difficult of digestion; to be offensive. [Low] [1913 Webster]