Boy Injured after Grenade Explosion at School

The video discusses a 15-year-old patient with severe injuries. His father, Rashid, wants to highlight the extent of his son's injuries. A planned surgery was canceled, and the patient's left leg is in a critical condition with no flesh remaining.

What does the phrase 'worst. No flash at all' imply about the injuries?

What can be inferred about the severity of the son's injuries?