The phrase "anesthetized animals" means animals that have been given medicine to make them unconscious or not feel pain during medical procedures or surgeries. Full definition
Cardiac catheterizations are performed in anesthetized animals and most commonly involve passing specialized catheters via either the jugular vein or carotid artery in the neck or femoral artery or vein in the leg into the great vessels and heart. (metropolitanvet.com)
After locating and chasing down a pack, an aerial sharpshooter would anesthetize an animal with a dart gun. (discovermagazine.com)
In this experiment, researchers anesthetize an animal and attach a small red dot to the middle of its forehead, where the dot will go unnoticed unless the animal can recognize itself in a mirror. (scientificamerican.com)