diff --git a/common/combat/harmful.trait.js b/common/combat/harmful.trait.js
index 43f2742..6ec9cfe 100644
--- a/common/combat/harmful.trait.js
+++ b/common/combat/harmful.trait.js
@@ -1,8 +1,6 @@
-import * as I from 'immutable';
-
-import {compose, invokeHookFlat, iterateForEach, merge} from '@avocado/core';
+import {compose} from '@avocado/core';
 import {StateProperty, Trait} from '@avocado/entity';
-import {fromRad, normalizeAngleRange, Vector} from '@avocado/math';
+import {Vector} from '@avocado/math';
 
 import {AFFINITY_PHYSICAL} from './constants';
 
@@ -32,8 +30,6 @@ export class Harmful extends decorate(Trait) {
 
   constructor(entity, params, state) {
     super(entity, params, state);
-    this._doesNotHarm = [];
-    this.locks = new Map();
     this._harmSpecs = this.params.harmSpecs.map((harmSpec) => {
       return {
         power: 0,
@@ -44,28 +40,6 @@ export class Harmful extends decorate(Trait) {
     });
   }
 
-  destroy() {
-    this.locks.clear();
-  }
-
-  doesNotHarmEntity(entity) {
-    if (!this.entity.isHarmful) {
-      return true;
-    }
-    return -1 !== this._doesNotHarm.indexOf(entity);
-  }
-
-  tryHarmingEntity(entity) {
-    if (this.doesNotHarmEntity(entity)) {
-      return;
-    }
-    if (entity.is('vulnerable')) {
-      if (!entity.isInvulnerable) {
-        this.entity.harm(entity);
-      }
-    }
-  }
-
   hooks() {
     return {
 
@@ -110,7 +84,7 @@ export class Harmful extends decorate(Trait) {
     const listeners = {};
     if (AVOCADO_SERVER) {
       listeners.collisionStart = (other) => {
-        this.tryHarmingEntity(other);
+        this.entity.harm(other);
       };
     }
     return listeners;
@@ -120,11 +94,17 @@ export class Harmful extends decorate(Trait) {
     return {
 
       harm: (entity) => {
-        if (this.locks.has(entity)) {
+        if (!this.entity.isHarmful) {
           return;
         }
-        if (this.params.harmLock > 0) {
-          this.locks.set(entity, this.params.harmLock);
+        if (!entity.is('vulnerable')) {
+          return;
+        }
+        if (!entity.isHarmedBy(this.entity)) {
+          return;
+        }
+        if (!entity.ensureVulnerabilityLock(this.entity, this.params.harmLock)) {
+          return;
         }
         for (let i = 0; i < this._harmSpecs.length; ++i) {
           const {power, type, variance} = this._harmSpecs[i];
@@ -170,19 +150,6 @@ export class Harmful extends decorate(Trait) {
         }
       },
 
-      setDoesHarm: (entity) => {
-        const index = this._doesNotHarm.indexOf(entity);
-        if (-1 !== index) {
-          this._doesNotHarm.splice(index, 1);
-        }
-      },
-
-      setDoesNotHarm: (entity) => {
-        if (-1 === this._doesNotHarm.indexOf(entity)) {
-          this._doesNotHarm.push(entity);
-        }
-      },
-
     };
   }
 
@@ -191,18 +158,9 @@ export class Harmful extends decorate(Trait) {
       if (this.entity.is('collider')) {
         const isCollidingWith = this.entity.isCollidingWith;
         for (let i = 0; i < isCollidingWith.length; i++) {
-          this.tryHarmingEntity(isCollidingWith[i]);
+          this.entity.harm(isCollidingWith[i]);
         }
       }
-      iterateForEach(this.locks.keys(), (key) => {
-        const remaining = this.locks.get(key) - elapsed;
-        if (remaining <= 0) {
-          this.locks.delete(key);
-        }
-        else {
-          this.locks.set(key, remaining);
-        }
-      });
     }
   }
 
diff --git a/common/combat/vulnerable.trait.js b/common/combat/vulnerable.trait.js
index 9305170..3727250 100644
--- a/common/combat/vulnerable.trait.js
+++ b/common/combat/vulnerable.trait.js
@@ -1,13 +1,13 @@
 import {Trait} from '@avocado/entity';
 import {
   behaviorItemFromJSON,
-  buildInvoke,
-  buildTraversal,
   Context,
 } from '@avocado/behavior';
-import {arrayUnique, flatten, invokeHookFlat} from '@avocado/core';
-import {hasGraphics, TextNodeRenderer} from '@avocado/graphics';
-import {randomNumber, Vector} from '@avocado/math';
+import {
+  arrayUnique,
+  invokeHookFlat,
+  iterateForEach,
+} from '@avocado/core';
 
 import {harmInteractions} from './harm';
 import {HarmPacket} from './harm.packet';
@@ -29,6 +29,12 @@ export class Vulnerable extends Trait {
     super(entity, params, state);
     this._harms = [];
     this._isInvulnerable = false;
+    this._isNotHarmedBy = [];
+    this.locks = new Map();
+  }
+
+  destroy() {
+    this.locks.clear();
   }
 
   acceptHarm(harm) {
@@ -272,6 +278,36 @@ export class Vulnerable extends Trait {
   methods() {
     return {
 
+      ensureVulnerabilityLock: (entity, duration) => {
+        if (this.locks.has(entity)) {
+          return false;
+        }
+        if (duration > 0) {
+          this.locks.set(entity, duration);
+        }
+        return true;
+      },
+
+      isHarmedBy: (entity) => {
+        if (this._isInvulnerable) {
+          return false;
+        }
+        return -1 === this._isNotHarmedBy.indexOf(entity);
+      },
+
+      setHarmedBy: (entity) => {
+        const index = this._isNotHarmedBy.indexOf(entity);
+        if (-1 !== index) {
+          this._isNotHarmedBy.splice(index, 1);
+        }
+      },
+
+      setNotHarmedBy: (entity) => {
+        if (-1 === this._isNotHarmedBy.indexOf(entity)) {
+          this._isNotHarmedBy.push(entity);
+        }
+      },
+
       vulnerabilityTypes: () => {
         const hookTypes = this.entity.invokeHookFlat('vulnerabilityTypes');
         return arrayUnique(hookTypes.concat(this.params.types));
@@ -280,4 +316,18 @@ export class Vulnerable extends Trait {
     };
   }
 
+  tick(elapsed) {
+    if (AVOCADO_SERVER) {
+      iterateForEach(this.locks.keys(), (key) => {
+        const remaining = this.locks.get(key) - elapsed;
+        if (remaining <= 0) {
+          this.locks.delete(key);
+        }
+        else {
+          this.locks.set(key, remaining);
+        }
+      });
+    }
+  }
+
 }