Which of the following is a clear indication of caffeine intoxication?

Caffeine intoxication is characterized by several clear physiological and psychological symptoms, with muscle twitching and tachycardia being common indicators. Caffeine is a central nervous system stimulant, and its overconsumption can lead to increased heart rates (tachycardia) and heightened levels of nervous system activity, which often manifest as muscle twitching or jitteriness. These symptoms reflect the overstimulation of the nervous system that caffeine can cause, distinguishing it from less specific or unrelated symptoms.

The other options present symptoms that do not align with caffeine intoxication. Slowed cognitive processing might occur due to fatigue or other factors but is contrary to the stimulating effects of caffeine. Excessive sleeping is also typically associated with depressants or fatigue rather than the stimulating properties of caffeine. Lastly, weight gain and lethargy are generally signs of an unhealthy lifestyle or metabolic issues rather than a state of caffeine intoxication. Thus, the presence of muscle twitching and tachycardia specifically correlates with the effects of caffeine consumption, marking it as a prime indicator of caffeine intoxication.