It turns out that pigs make arbitrary decisions for some of the same reasons humans do. They get moody and peevish, and they allow those feelings to dictate judgement. By subjecting pigs to a series of experiments involving chocolate candies and uncomfortable beds, a group of UK researchers determined that pigs have some of the same psychological blind spots as humans.

Scientists have long known that humans suffer from cognitive biases that stem from our fundamental personalities interacting with more transient moods. University of Newcastle neuroscientist Lucy Asher and colleagues explain in a Biology Letters paper that pig personalities can be grouped into two groups: proactive and reactive. Proactive pigs tend to be extroverted, inflexible, and optimistic, while reactive ones are neurotic and easily affected by their environments. The researchers did personality tests on 36 pigs to determine whether they were proactive or reactive and then put them in a variety of situations where they had to make split-second decisions about whether to seek out a hidden treat.

Here's how it worked. For several days in a row, the pigs were given a dish with a false bottom that contained three delicious chocolate candies. The dish would always be put in the exact same spot. At the same time, the pigs were given a similar dish with much-loathed (among pigs) coffee beans under the false bottom. The disgusting coffee dish was also placed in a distinctive spot. After a while, the pigs learned to make a beeline for the dish in the chocolate spot and ignore the dish in the coffee spot. (Both dishes had been coated in sugar, so they smelled the same.) These learning sessions also gave the researchers a sense of how quickly the pigs would move toward the dish if they felt optimistic about finding a hidden tasty treat.

Then they completely rocked the pigs' worlds. They started putting out dishes in new places in between the chocolate and coffee spots to introduce uncertainty. To find out whether mood and personality would affect what pigs did, they then changed one more thing. They put some of the pigs into big pens with toys and fluffy straw beds. They put others into smaller pens with no straw. The pigs without straw beds were noticeably less pleased with their accommodations and were put into rather bad moods.

Next came the true test of pig personality and mood. Would the environment affect the proactive and reactive pigs differently, thus showing a mixture of mood and personality in decision-making? It did indeed. Proactive pigs' generally optimistic outlook was mostly unaffected by their less cushy digs. They approached most dishes as if they were treat dishes, moving quickly to open the false bottoms. That said, they didn't forget their old lessons. The closer the dish was to the coffee spot, the less likely they were to act quickly. The reactive pigs, on the other hand, were so bothered by their uncomfortable beds that they didn't even bother to approach dishes that weren't in the chocolate spot. They had a decidedly pessimistic reaction, deciding that any dish outside the chocolate spot was probably an awful coffee dish. Why bother even checking?

What's fascinating here is that we're seeing fairly complex emotional behavior. The proactive pigs and reactive pigs weren't just acting on personality traits. Their decisions depended on circumstance. Uncomfortable pens caused bad moods—and those moods interacted with their personalities to dictate behavior. Put a group of pigs into terrible circumstances, where all they get are hard beds and coffee, and they won't all react the same way. Some will sink into pessimism, while others will soldier onward, hoping to find chocolates hidden in new places.

Biology Letters, 2016. DOI: 10.1098/rsbl.2016.0402