Typical Aztec sacrafice, using a tecpatl
The Tecpatl was a sacrificial knife used by the Aztecs. It was the Short-Range weapon of the Aztec Jaguar.
Description
The Tecpatl consisted of a double-sided obsidian blade attached to a short wooden handle. In more ceremonial examples, the handle would be intricately carved.
Use
The Tecpatl was primarily used for human sacrifice, an important part of Aztec society which essentially forced them to constantly wage war on surrounding peoples and take them prisoner. Although it may have only seen limited use on the battlefield, it's sharp edges would have made it an effective sidearm.