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Can Predators be Uninterested and Even Friendly with their Prey?

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We are all very familiar with Tom’s incessant chase for Jerry, as well as Jerry’s clever and funny ways to avoid being caught by his raider. However, new scientific experiments have challenged the famous notion of mice fearing cats. Scientifics argue that a chemical change that stops mice from fearing cats makes them immune to their predators, since they can only attack mice when they sense their fear. Furthermore, they argue that, if applied to other animals, this scientific finding could be the end to predators’ attack on their preys. However, explanations for the ways in which fear is sensed by the predators are contradictory and even suggest that it is because of the expression of fear that preys are attacked and not because predators are meant to attack them.

Scientists at Tokyo University have described the reason behind their success in making mice immune to cats. They explained that because cats only attack mice when they sense their fear, they created “fearless mice by shutting down receptors in their olfactory bulb”; the olfactory bulb is the part of the brain that is in charge of processing smells [1].These receptors in the mice’s ‘olfactory bulb’ are what make mice fear cats, as Kobayakawa, the scientist behind this experiment further explained, “Mice fear cats because they are innately conditioned to fear when sensing the odor of the predators. So by getting rid of the specific receptors for sensing the odor, mice never feel afraid of cats” [2]. Thus, it is argued that the results from this experiment support the “long-held-belief among scientists that fear in animals is connected to their keen sense of smell” [1]

So, does the ‘smell of fear’ really exist?

Although the notion of the smell of fear is very well known and accepted, recent studies challenge this belief. As suggested in a literary research, “Taken literary, this statement seems absurd”.  It is hard to imagine that an emotion, fear, can have a characteristic from a substance, smell [3]. But to understand how this concept can be so well accepted by scientists we must look at the part in our bodies that perceives odors, the olfactory system. There are two divisions of the olfactory system. One of them in charge of the conscious recognition of smells, the one that recognizes specific smells, like the smell of the brewing coffee. The second one, is the accessory olfactory system, which is designed to “’read’ the messages of non-volatile pheromones, communicative chemicals emitted by all animals” [4].

Both of the divisions of the olfactory system project to the limbic system through their nerves. The limbic system is “the part of the brain that deals with emotional perception and response” [4]. Particularly, the limbic system’s primary organ, the amygdale, is directly in charge of ‘perceiving and responding to fear’. Therefore, this close response from the olfactory system to the limbic system suggests that fear might in fact be transmitted by smell. Nevertheless, the belief that “pheromone communication via the accessory system is possible only within animals of the same species” discards the story of the ‘smell of fear’ that the cat might sense from the mice [4]. Instead, a research suggests that the odors released by some animals are actually the ‘smell of danger’.

The recognition of an unfamiliar scent is what possibly causes an animal to attack. The unfamiliar scent released by some animals may be caused by its emotional state. As explained, “Studies have demonstrated that fear and emotional stress are conditions which may be communicated in mice and rats” [3]. These signals that the animals produce under stress are meant to “function as a warning to others after danger has been encountered, rather than being the cause of a dangerous encounter” [3].  Thus, when detecting an unusual odor, predators are alarmed about a possible danger, but it takes more than the sense of a strange odor for them to attack.

Studies suggest that behavioral cues are what make animals react in different ways (depending on the level of danger that they feel that they are exposed). As a researcher explains, “If a frightened or nervous person approaches a horse, …the animal’s ability to perceive this fear may help it avoid rough handling” [4]. Although there is not enough documentation on the animals’ behavior when they are scared, some researchers argue that it is behavioral clues what makes predators discern fear in their prey. Another researcher who shares the same notion provides the example of predatory cats, and explains, “Seeing a small object running away is considered to be the stimulus for chasing … Therefore, a cat can quickly detect a panic-stricken mouse through visual stimuli alone” [3]. We can also see this reaction when someone approaches a honeybee hive, the bees sense an unfamiliar odor and if the person in response to a possible fear of bees moves unsteadily, the bees will probably attack him [3]. Thus, it isn’t one factor alone that makes predators react and attack their victims; it is a combination of both the ‘smell of danger’ and behavioral cues.

Both of these factors, odor and behavioral cues are what determine a predators attack. However, the fact that the predator had to first be alerted of a possible danger by an unfamiliar odor, and finally react to unexpected movements or actions by the other animal suggests that predators might not even mean to harm the prey in the first place. Thus, the scientists’ experiment in making mice unable communicate fear to the cat supports the story that predators only attack in response to possible danger. This experiment, if developed further, as Kobayakawa intends, could prevent endangered species from being attacked by predators.




[1],,2226236,00.html#article_continue – “Japanese Scientists Create Mice with no Fear of Cats”, Guardian Unlimited.

[2] - “Scientists Create Mice with No Fear of Cats”, Itchmo: News for Dogs & Cats.

[3] -“Can Animals Really Smell Fear?” University of South Carolina

[4] -“Can Animals Really Smell Fear?” Research Penn State