What is "shaking piece"

Shake \Shake\, v. i. To be agitated with a waving or vibratory motion; to tremble; to shiver; to quake; to totter.

Under his burning wheels The steadfast empyrean shook throughout, All but the throne itself of God.
--Milton.

What danger? Who 's that that shakes behind there?
--Beau. & Fl.

Shaking piece, a name given by butchers to the piece of beef cut from the under side of the neck. See Illust. of Beef.