Unless a direct hit is made to a primary artery near the surface (carotid, femoral, brachial, etc.), blood does not immediately come from a wound. Even a direct puncture wound to the heart wouldn't erupt blood the way it does in the movies. Every time I have treated gunshot and penetration wounds to the chest, the blood oozed (granted, with varying degrees of rapidity depending on how large the hole and how many arterial and venal structures were compromised), it didn't spurt. Even with a wide blade such as a Gladius Pompeianus (which is what that appears to be, though during the Gallic Wars they would have used either Hispaniensis or Mainz, that may be a Brythonic warrior, not a Gaul; the artist would have to clarify that one), blood does not emerge from the wound until the blade is withdrawn as the blade itself helps to seal the wound and prevent hemorrhaging. That is one of the reasons we tend to leave penetrating objects in the wound (in addition to being able to determine the wound track via X-ray) when administering treatment. When it comes to weapons, wounds, and realism, Hollyweird is a bad influence on the public consciousness