Cat
The stress-reducing properties of cats have been subjected to considerable scientific scrutiny. Cat ownership correlates with reduced cardiovascular disease risk and lower baseline cortisol levels. The feline purr, oscillating between 25 and 150 hertz, has been associated with measurable calming effects in human listeners. The rhythmic motion of stroking a cat's fur engages meditative neural pathways. However, cats also introduce stressors: veterinary emergencies, furniture destruction, and the 3 AM vocalisation demanding breakfast. The cat's stress reduction arrives packaged with stress creation of approximately equivalent magnitude.
Tetris
Tetris presents a more complex stress profile. The game has demonstrated clinical efficacy in reducing anxiety and PTSD symptoms—a 2017 study showed that Tetris play following traumatic events reduced subsequent flashback frequency. The cognitive engagement required displaces anxious rumination. However, Tetris simultaneously generates its own stress through increasing difficulty curves and the perpetual threat of the dreaded 'topping out.' The game offers stress relief only insofar as its own stressors eclipse whatever preceded them. This is stress substitution rather than stress reduction.