Which of the following is a psychophysical indicator of inhalant use?

B. Slurred speech is a psychophysical indicator of inhalant use because inhalants can affect the central nervous system, leading to impairment in coordination, communication, and cognitive functions. Slurred speech typically indicates a decrease in the ability to articulate words clearly, which is often observed in individuals under the influence of substances that depress the nervous system. Inhalants can lead to a range of symptoms that mimic alcohol intoxication, including confusion, lethargy, and impaired motor functions.

In contrast, increased focus may suggest heightened alertness, which is not typically associated with inhalant use. A calm demeanor might be seen in some contexts but does not specifically indicate inhalant use as it can be influenced by various other factors. Enhanced motor skills are also unlikely as inhalants generally impair motor coordination rather than improve it. Thus, slurred speech stands out as an unmistakable psychophysical sign of inhalant consumption.