Rennet, the stomach contents of an unweaned animal; also, the membrane lining the stomach. The word rennet also refers to preparations that contain the enzyme rennin and that are used in curdling milk. The chief source of rennet is the fourth stomach of young calves. Rennet is used in making cheese, junket, and medicinal preparations. It is also used to coagulate casein (a milk protein) in making plastics.
Mockingbird is a bird related to the catbird and thrasher. Its natural song is a series of clear, varied notes, usually repeated several times, but it is named for its ability to imitate the songs of other birds is and even the mewing of cats.
Sharks have been around longer than the dinosaurs. After a few hundred million years, it's humans that might kill them off.