A trainer for practicing an intraosseous infusion is presented. The trainer includes a mannequin and an injection-site simulant. The mannequin is in the form of a body, human or animal, in part or whole. The injection-site simulant further includes a pocket, an insert, and an outer cover. The pocket extends into the mannequin. The insert simulates a hard exterior of a bone. The insert is disposed within the pocket. The outer cover with a plug simulates a skin, human or animal. The outer cover conceals the insert, the pocket, and the plug. The pocket and the insert cooperate to form a cavity. The cavity is disposed where marrow resides within the bone. The cavity is capable of receiving a fluid injected through a hole formed during use through the outer cover, the plug, and the insert. The plug sealingly contacts and cooperates with at least one of the insert or the wall within the pocket to confine the fluid within the cavity.