Swoopo is addictive not because of sunk cost (as we have argued here) but because it impacts dopamine levels in the brain, says writer Jonah Lehrer of The Frontal Cortex, a science blog. Lehrer writes this fascinating article comparing the results of a scientific experiment - one where the impact of a reward on dopamine levels in monkey brains was tested under various circumstances - to Swoopo. In the study Lehrer describes, scientists found that monkeys responded to the expectation of a reward (apple juice) with an increased flow of dopamine to the brain, the same increase in dopamine as when the juice was actually received. However, once the monkeys became conditioned to expect the juice, their brains no longer responded with a dopamine spike, neither to the expectation nor to actually receiving the juice. The study concludes that neurons are concerned with expected rewards more so than actually receiving a reward. This applies to Swoopo, Lehrer writes, because bidders are kept in a state of perpetual expectation. Every time a user places a bid he becomes the high bidder and hopes/expects to win the item. According to the monkey experiment, this act causes dopamine levels to spike and since the reward is never guaranteed the brain is kept in a state of perpetual suspense, which stops the dopamine spike from diminishing over time. This spiking of the "happiness" chemical in the brain is what causes people to bid over and over and over again, says Lehrer.
Apart from being interesting, Lehrer's article adds legitimacy to Swoopo's claim that the site offers "entertainment shopping," for better or worse.