The best explanation for Khalil's improved performance when he was taking the herbal medicine is the Placebo Effect. Sugar and basil leaves in the amount that a medicine dose contains would not have any significant effect on Khalil's performance, but the placebo effect can cause someone to see improvements from a placebo (a treatment with no active effect) simply because they expect to see improvements. Since Khalil expected improvements from taking the medicine, he might have perceived improvements from the placebo effect even though the medicine had no real effect.