Answer:
The effect that alcohol has on the brain.
Step-by-step explanation:
Alcohol is one of the few substances that can get into contact with brain cells and affect them directly which results in behavioral change when exposed to too much alcohol.
The example given in the question is a result of that. Reynaldo acting very different than his normal self and becoming verbally abusive and showing agressive behavior is a sign that the alcohol is affecting his Frontal Lobe.
This is the part of the brain that is assigned with the control of very important functions such as emotional behavior, making decisions, language abilities etc. and when it is affected by alcohol, it can lead to unexpected emotional expressions such as fighting, crying etc.
I hope this answer helps.