I'm a vet tech at a cat clinic and I assist with these same procedures on domestic cats two or three times a week. It's fascinating to see how similar it is for big cats. It's not super unusual for cats to pause breathing when you first put them under (though it's more common in dogs), but it's always unnerving or downright alarming when it's not just a pause. On an animal as old as that lion, you would ideally want to do a full exam and bloodwork before anesthetizing him to make sure he doesn't have kidney, heart, or lung problems that would make anesthesia dangerous. Unfortunately, you can't do that with animals that have so much potential to injure you, like big or extremely angry cats.
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