headcrabsdontexist = false

function NoHeadcrabs(bool)
	if(bool) then headcrabsdontexist = true end
	if(!bool) then headcrabsdontexist = false end
end
	
local function RemoveCrabsTick()
	if(headcrabsdontexist) then
        local Crabs = table.Add( table.Add( table.Add( table.Add( ents.FindByClass( "npc_headcrab" )), ents.FindByClass( "npc_headcrab_fast" ) ), ents.FindByClass( "npc_headcrab_black" ) ), ents.FindByClass( "npc_headcrab_poison" ))
		local Zombies = table.Add(table.Add( table.Add( table.Add( table.Add( ents.FindByClass("npc_zombie_torso"), ents.FindByClass( "npc_zombie" )), ents.FindByClass( "npc_fastzombie" ) ), ents.FindByClass( "npc_zombine" ) ), ents.FindByClass("npc_fastzombie_torso")), ents.FindByClass("npc_poisonzombie"))
            for _, crab in pairs( Crabs ) do
                SafeRemoveEntity( crab )
            end
			for k, zombie in pairs( Zombies ) do
                zombie:SetBodygroup(1,0)
				zombie:SetBodygroup(2,0)
				zombie:SetBodygroup(3,0)
				zombie:SetBodygroup(4,0)
            end
		end
    end   
hook.Add( "Tick", "NoHeadcrabsTick", RemoveCrabsTick )

local function HeadcrabsStay(ent,dmg)
if(headcrabsdontexist) then
	if (IsValid(ent) && ((ent:GetClass() == "npc_zombie") || (ent:GetClass() == "npc_zombine") || (ent:GetClass() == "npc_fastzombie") || (ent:GetClass() == "npc_zombie_torso") || (ent:GetClass() == "npc_fastzombie_torso") || (ent:GetClass() == "npc_poisonzombie"))) then
		--Get zombie data
		local Data = ent:GetSaveTable()
		--Check if this shot will kill them
		local HP = ent:Health()
		if dmg:GetDamage()>=HP then
			--We will die, change things that we need to to prevent headcrabs
			--increase damage to prevent headcrabs if needed
			local MaxHP = Data.max_health or 100
			if dmg:GetDamage()<MaxHP then
				dmg:SetDamage(MaxHP*2) --Increase damage to ensure no headcrab (this _should_ only need to be >= 25% of MaxHP)
			end
			dmg:SetDamageType(DMG_SLASH)
			--Return modified damage
			return dmg
		end
	end
end
end
hook.Add("EntityTakeDamage", "Headcrabs Stay", HeadcrabsStay)