diff --git a/README b/README
index 7de38c7..937314b 100644
--- a/README
+++ b/README
@@ -57,10 +57,11 @@ The following outputs are supported:
 
 	move_dir <x> <y>
 		<x> and <y> are integer offsets relative
-		to the current position; may be just {-1,0,1}
-	attack_dir <x> <y>
+		to the current position, may be just {-1,0,1}
+	attack_dir <x> <y> <force>
 		<x> and <y> are integer offsets relative
-		to the current position; may be just {-1,0,1}
+		to the current position, may be just {-1,0,1};
+		<force> is invested energy, damage is proportional
 	breed_dir <x> <y> <info>
 		<info> is arbitrary string passed to the "mother"
 		(to be passed to the child)
@@ -105,3 +106,6 @@ If the id corresponds to a disconnected agent, the connection
 is immediately attached to that agent. Combining this with other
 negotiation commands is undefined, except for newborns - in that case,
 negotiation commands must follow after agent_id.
+
+TODO proto. change:
+	tickid for input
diff --git a/agent.cc b/agent.cc
index 2b117ce..237a341 100644
--- a/agent.cc
+++ b/agent.cc
@@ -66,7 +66,7 @@ agent::move_dir(int dir_x, int dir_y)
 }
 
 bool
-agent::attack_dir(int dir_x, int dir_y)
+agent::attack_dir(int dir_x, int dir_y, int force)
 {
 	if (dead || !tile)
 		return false;
@@ -76,8 +76,8 @@ agent::attack_dir(int dir_x, int dir_y)
 		return false;
 
 	class agent *a = t2->agent;
-	chenergy(world::attack_cost);
-	a->chenergy(world::defense_cost);
+	chenergy(-force);
+	a->chenergy(-force * world::defense_const_factor);
 	if (dead || a->dead)
 		return true;
 
@@ -86,9 +86,10 @@ agent::attack_dir(int dir_x, int dir_y)
 	int attack_roll = random() % attack_dice;
 	int defense_dice = round(a->attr.defense * a->energy);
 	int defense_roll = random() % defense_dice;
-	if (attack_roll > defense_roll)
-		a->chenergy(defense_roll - attack_roll);
-	return attack_roll >= defense_roll;
+	if (attack_roll > defense_roll) {
+		a->chenergy(-force);
+	}
+	return attack_roll > defense_roll;
 }
 
 bool
diff --git a/agent.h b/agent.h
index 747c8bf..c900f62 100644
--- a/agent.h
+++ b/agent.h
@@ -58,7 +58,7 @@ public:
 	void spawn_at(class tile &tile);
 
 	bool move_dir(int dir_x, int dir_y);
-	bool attack_dir(int dir_x, int dir_y);
+	bool attack_dir(int dir_x, int dir_y, int force);
 	bool breed_dir(int dir_x, int dir_y, std::string info);
 	bool secrete(int id, double intensity);
 
diff --git a/client/example.pl b/client/example.pl
index 60e5547..9bbc82f 100755
--- a/client/example.pl
+++ b/client/example.pl
@@ -116,7 +116,7 @@ sub take_action($$) {
 	print "moves ".join(", ", @move)." => (".dirindex($max).":$max->[0],$max->[1])\n";
 
 	if ($attack[dirindex($max)]) {
-		print $socket "attack_dir $max->[0] $max->[1]\r\n";
+		print $socket "attack_dir $max->[0] $max->[1] 100\r\n";
 	} else {
 		print $socket "move_dir $max->[0] $max->[1]\r\n";
 	}
diff --git a/connection.cc b/connection.cc
index 64b9403..eaa90f6 100644
--- a/connection.cc
+++ b/connection.cc
@@ -168,11 +168,12 @@ bump_negot:
 				bump();
 			mask |= 1;
 		} else if (!negotiation && !cmd.compare("attack_dir") && !(mask & 2)) {
-			int x = 0, y = 0;
-			sscanf(line.c_str(), "%d %d", &x, &y);
+			int x = 0, y = 0, force = 0;
+			sscanf(line.c_str(), "%d %d %d", &x, &y, &force);
 			if (x < -1) x = -1; if (x > 1) x = 1;
 			if (y < -1) y = -1; if (y > 1) y = 1;
-			if (!agent->attack_dir(x, y))
+			if (force < 1) force = 1;
+			if (!agent->attack_dir(x, y, force))
 				bump();
 			mask |= 2;
 		} else if (!negotiation && !cmd.compare("breed_dir") && !(mask & 4)) {
diff --git a/world.h b/world.h
index ac21459..d24ccb9 100644
--- a/world.h
+++ b/world.h
@@ -7,8 +7,6 @@ struct world {
 	const static int max_energy = 20000;
 
 	const static int move_cost = -50;
-	const static int attack_cost = -400;
-	const static int defense_cost = -200;
 	const static int breed_out_cost = -newborn_energy/4;
 	const static int breed_in_cost = -newborn_energy*3/4;
 	const static int pheromone_cost = -10;
@@ -19,6 +17,8 @@ struct world {
 	const static int sun_energy = 10;
 	const static int soil_energy = 20; /* ... times five for lone herbs, times one for dense forests */
 
+	const static double defense_const_factor = 0.2;
+
 	const static int dead_body_energy = 2000;
 	const static double dead_body_energy_carryover = 0.5;
 	const static int dead_decay = -50;