The Giant singles out a lone enemy and 'eadbutts them. Nominate a single model in the fighting rank of an enemy unit the Giant is engaged with to be the target of this attack. That model is hit and suffers D3+1 wounds with no armour or Regeneration saves permitted (Ward saves can be attempted as normal).
The Bonegrinder Giant squints angrily at their enemy and ’eadbutts them. The target unit suffers a single hit and suffers D3+1 wounds with no armour or Regeneration saves permitted (Ward saves can be attempted as normal).