Other symptoms
Besides lack of speech, other common behaviors and characteristics displayed by selectively mute people, according to Dr. Elisa Shipon-Blums findings, include:
Shyness, social anxiety, fear of social embarrassment or social isolation and withdrawal
Difficulty maintaining eye contact
Blank expression and reluctance to smile or incessant smiling
Difficulty expressing feelings, even to family members
Tendency to worry more than most people of the same age
Sensitivity to noise and crowdsOn the flip side, there are some positive traits observed in many cases:

Above average intelligence, inquisitiveness, or perception
A strong sense of right and wrong
Creativity
Love for the arts
Empathy
Sensitivity for other people

Causes
Selective mutism (SM) is an umbrella term for the condition of otherwise well-developed children or adults who cannot speak or communicate under certain settings. The exact causes that affect each person may be different and yet unknown. There have been attempts to categorize, but there are no definitive answers yet due to the under-diagnosis and small/biased sample sizes. Many people are not diagnosed until late in childhood only because they do not speak at school and therefore fail to accomplish assignments requiring public speaking. Their involuntary silence makes the condition harder to understand or test. Parents often are unaware of the condition since the children may be functioning well at home. Teachers and pediatricians also sometimes mistake it for severe shyness or common stage fright.Most children and adults with selective mutism are hypothesized to have an inherited predisposition to anxiety. They often have inhibited temperaments, which is hypothesized to be the result of over-excitability of the area of the brain called the amygdala.
There is no specific antidote to barbiturate overdose; treatment is supportive, generally  including the administration of intravenous saline, naloxone, thiamine, glucose, sodium bicarbonate to alkalize the urine and increase rate of excretion, and activated charcoal via nasogastric tube.Acetaminophen exerts its toxicity through the production of a toxic metabolite that can cause liver damage at doses as low as four grams. Larger doses can precipitate acute liver failure, acute kidney injury, or gastrointestinal bleeding; death has been known to occur with ingestion of ten to fifteen grams. The specific antidote to acetaminophen overdose is N-acetylcysteine. Mechanism of action
Butalbital exerts a generalized depressant effect on the central nervous system and, in very high doses, has peripheral effects. Acetaminophen has analgesic and antipyretic effects mediated by a metabolite that acts at cannabinoid receptors. Caffeine is thought to produce constriction of cerebral blood vessels and serves to counteract the sedative effect of butalbital.Butalbital has a half-life of about 35 hours. Acetaminophen has a half-life of about 1.25 to 3 hours, but may be increased by liver damage and after an overdose. Caffeine has a half-life of about 2.5 to 4.5 hours. References
External links
"Acetaminophen mixture with butalbital". Drug Information Portal. U.S. National Library of Medicine. "Acetaminophen mixture with butalbital and caffeine". Drug Information Portal. U.S. National Library of Medicine.