Once in the brain, alcohol affects all of the following critical skills EXCEPT:

Alcohol is known to impair various critical functions in the brain, including memory recall, coordination, and mood regulation. However, blood flow is not a skill or cognitive function that alcohol directly affects in the same way. Instead, alcohol can influence blood pressure and vascular response, but these changes are not categorized under critical skills.

Memory recall is largely impacted by alcohol as it interferes with the hippocampus' ability to form new memories. Coordination is also significantly affected since alcohol impairs the cerebellum, which is responsible for motor control and balance. Mood regulation is another area where alcohol has a pronounced influence, often leading to alterations in emotional states and behavior due to its action on neurotransmitters.

In contrast, while blood flow can change due to the physiological effects of alcohol consumption, it does not fall under the realm of cognitive or physical skills that alcohol impairs. Therefore, this aspect distinguishes blood flow from the other critical skills listed.