(CNN) There's a popular thought experiment called the "trolley problem" that attempts to explore an impossible question:
How valuable is a life?
You imagine yourself driving a trolley down a fixed track. Five people are immobilized in your path. If you continue, they'll surely die. If you pull a lever, the trolley will switch to another track, but you'll kill a single person standing there.
Do you do nothing and guarantee one tragedy, or do something -- anything -- and create another?
Zookeepers at the Cincinnati Zoo had to make such a choice when a 3-year-old boy slipped into the habitat of a silverback gorilla. After a teeth-clenching 10-minute encounter, keepers shot and killed the 450-pound gorilla, Harambe. The boy survived.
The decision clearly valued the life of the child.
Public response, for the most part, was more concerned with the animal.
For days, the Internet was saturated with think pieces and tributes. The boy's family was barraged with accusations and calls for criminal charges.
Was Harambe's death the tragic result of bad parenting? Who should pay? Whose lives had Harambe touched?
All these questions lead to another: What causes us to mourn for, and rage on behalf of, an animal who died so a child could live?
"The real reason why humans get so intense about the killing of a gorilla is the same reason we get mad when children or infants die," says Kurt Gray, assistant professor of psychology and neuroscience at the University of North Carolina Chapel Hill .
Gray says we see minds in two different ways.
"One way is as an agent, a thinking doer, if you will," he says. "The other is as a vulnerable feeler. And those minds suffer and sense."
Babies, gorillas, animals in general -- they all fall into the latter category.
"Animals seem so vulnerable, people feel the need to protect them," Gray says.
You would think video of the harrowing incident at the Cincinnati Zoo would provide some decisive evidence of what happened. That's proven difficult, because we have a tendency to anthropomorphize.
Was Harambe dragging the boy through the water, or carrying him? When he pulled the boy up by the pants, was he feeling threatened? Protective? Confused?
"From what we saw [the child] could have been killed at any second," one witness told CNN affiliate WCPO.
Contrast that with what famed primatologist Jane Goodall said. "It looked as though the gorilla was putting an arm round the child."
It's easy to ascribe intent, Gray says.
"Our tendency is to see our actions through human lenses," Gray says. "We can't imagine what it's like to actually be a gorilla. We can only imagine what it's like to be us being a gorilla."
Harambe is the de facto emotional successor of Cecil the Lion, who was shot, skinned and decapitated outside a Zimbabwean national park last year.
Walter Palmer, the lion's killer, became an uncontested villain. Actually, far more than a villain -- the dentist's very humanity was questioned. Some said, outright, that he too should be hunted down and flayed.
The online mob also came for Kendall Jones, a Texas cheerleader and hunting enthusiast who posted pictures on Facebook of her posing next to slain leopards, hippos and mountain lions. The responses ranged from relatively mild ("Mr. Zuckerberg, take down her page!") to vicious ("Is there any way to hunt you?").
Our rush to empathize and defend lessens the more we perceive another mind to be an agent rather than an innate victim. When Harambe died, someone else had to be responsible since Harambe himself couldn't make ethical decisions. When a dentist or a cheerleader takes the life of an animal, critics see the act as reprehensible because animals are "innocent."
But from time to time, our predisposition to fight for animals slides into satire.
Two years ago, people were so enraged by a picture of Steven Spielberg posing in front of a dead animal he had been accused of killing, they failed to notice it was actually a triceratops prop from the original "Jurassic Park." While most of the 12,000 comments on the photo are satirical, some express rage -- genuine, unchecked rage -- at the "killing" of an animal that hasn't roamed the planet in 66 million years.
CNN Legal Analyst Laura Coates says this irrational vulnerability we seem to have for animals extends to the actual courtroom.
As a prosecutor, she'd had to recount for a jury the gruesome acts of a rapist or a murderer on trial.
"Strangely, when I would relay even the most horrific details, the reaction by juries was always tempered," she says. "But when I had an animal as victim? Please. I could have simply held up a dog biscuit during my opening statement and secured a unanimous verdict within minutes."
Coates uses this striking example to make her point. The petition calling for a criminal investigation into the parents of the boy who tangled with Harambe has nearly 330,000 signatures. A petition calling for justice for 12-year-old Tamir Rice, who was shot and killed by police while holding a toy gun, has about half as many.
"Frankly, the level of concern that one would expect for an act against a human child pales in comparison to the universal cries for justice when an animal is hurt," she wrote for CNN.
In both the deaths of Harambe and Tamir Rice, a decision was made and a lever was pulled.
Only one cost a human life.