Prof Bekoff's research into the sentience of animals reported on the stress, fear and boredom animals experience when confined in claustrophobic zoo enclosures that can be one millionth the size of their natural ranges. "They'll feel the exact same emotions as companion animals - dogs and cats - if they're just kept locked up," he says. This is backed up by a study which found that elephants in zoos often endure stress and have significantly shorter life spans than wild elephants. Then there are the horror-story incidents: Harambe the gorilla was shot and killed in 2016 after dragging a toddler who'd climbed into an enclosure at Cincinnati Zoo; Tilikum the orca killed trainer Dawn Brancheau at Sea World Orlando; London Zoo keeper Jim Robson was killed by an elephant in front of a packed crowd in 2001.