diff --git a/agent.cc b/agent.cc
index cb06493..7a10765 100644
--- a/agent.cc
+++ b/agent.cc
@@ -114,6 +114,7 @@ agent::on_tick(void)
 
 	if (!dead) {
 		chenergy(world::sun_energy);
+		chenergy(attr.move * world::move_idle_cost);
 
 	} else {
 		energy += world::dead_decay;
diff --git a/world.h b/world.h
index b2266fd..a8e0687 100644
--- a/world.h
+++ b/world.h
@@ -6,6 +6,8 @@ struct world {
 	const static int move_cost = -50;
 	const static int attack_cost = -400;
 	const static int defense_cost = -200;
+
+	const static int move_idle_cost = -15; /* ... * attr.move */
 	const static int sun_energy = 10;
 
 	const static int dead_body_energy = 2000;