If you’re in the market for new friends, you can administer a simple compatibility test.
If your companion does not yawn, locate the exit. You might be with a psychopath.
Apparently contagious yawning is the norm for most mammals. But Baylor University researchers found that people with psychopathic tendencies (cold-hearted, no empathy) will be unaffected by a companion’s yawn.
In other words, friends don’t let friends yawn alone.