diff --git a/OpenRa.Game/Traits/Activities/Attack.cs b/OpenRa.Game/Traits/Activities/Attack.cs
index f059af9a7e..1e2b633d74 100644
--- a/OpenRa.Game/Traits/Activities/Attack.cs
+++ b/OpenRa.Game/Traits/Activities/Attack.cs
@@ -19,7 +19,7 @@ namespace OpenRa.Game.Traits.Activities
 
 		public IActivity NextActivity { get; set; }
 
-		public IActivity Tick( Actor self, Mobile mobile )
+		public IActivity Tick( Actor self )
 		{
 			var unit = self.traits.Get<Unit>();
 
@@ -44,7 +44,7 @@ namespace OpenRa.Game.Traits.Activities
 			return null;
 		}
 
-		public void Cancel(Actor self, Mobile mobile)
+		public void Cancel(Actor self)
 		{
 			Target = null;
 		}
diff --git a/OpenRa.Game/Traits/Activities/DeliverOre.cs b/OpenRa.Game/Traits/Activities/DeliverOre.cs
index cf75faffed..89e3e7db4a 100644
--- a/OpenRa.Game/Traits/Activities/DeliverOre.cs
+++ b/OpenRa.Game/Traits/Activities/DeliverOre.cs
@@ -21,9 +21,10 @@ namespace OpenRa.Game.Traits.Activities
 
 		static readonly int2 refineryDeliverOffset = new int2( 1, 2 );
 
-		public IActivity Tick( Actor self, Mobile mobile )
+		public IActivity Tick( Actor self )
 		{
 			var unit = self.traits.Get<Unit>();
+			var mobile = self.traits.Get<Mobile>();
 
 			if( isDone )
 			{
@@ -74,7 +75,7 @@ namespace OpenRa.Game.Traits.Activities
 			return null;
 		}
 
-		public void Cancel(Actor self, Mobile mobile)
+		public void Cancel(Actor self)
 		{
 			// TODO: allow canceling of deliver orders?
 		}
diff --git a/OpenRa.Game/Traits/Activities/DeployMcv.cs b/OpenRa.Game/Traits/Activities/DeployMcv.cs
index 02ae60be48..bd08bd44c8 100755
--- a/OpenRa.Game/Traits/Activities/DeployMcv.cs
+++ b/OpenRa.Game/Traits/Activities/DeployMcv.cs
@@ -9,7 +9,7 @@ namespace OpenRa.Game.Traits.Activities
 	{
 		public IActivity NextActivity { get; set; }
 
-		public IActivity Tick( Actor self, Mobile mobile )
+		public IActivity Tick( Actor self )
 		{
 			Game.world.AddFrameEndTask( _ =>
 			{
@@ -19,7 +19,7 @@ namespace OpenRa.Game.Traits.Activities
 			return null;
 		}
 
-		public void Cancel( Actor self, Mobile mobile )
+		public void Cancel( Actor self )
 		{
 			// Cancel can't happen between this being moved to the head of the list, and it being Ticked.
 			throw new InvalidOperationException( "DeployMcvAction: Cancel() should never occur." );
diff --git a/OpenRa.Game/Traits/Activities/Follow.cs b/OpenRa.Game/Traits/Activities/Follow.cs
index 18e4304a6b..f7433f3835 100644
--- a/OpenRa.Game/Traits/Activities/Follow.cs
+++ b/OpenRa.Game/Traits/Activities/Follow.cs
@@ -18,7 +18,7 @@ namespace OpenRa.Game.Traits.Activities
 
 		public IActivity NextActivity { get; set; }
 
-		public IActivity Tick( Actor self, Mobile mobile )
+		public IActivity Tick( Actor self )
 		{
 			if (Target == null || Target.IsDead)
 				return NextActivity;
@@ -29,7 +29,7 @@ namespace OpenRa.Game.Traits.Activities
 			return null;
 		}
 
-		public void Cancel(Actor self, Mobile mobile)
+		public void Cancel(Actor self)
 		{
 			Target = null;
 		}
diff --git a/OpenRa.Game/Traits/Activities/Harvest.cs b/OpenRa.Game/Traits/Activities/Harvest.cs
index 8caa545956..c1c88bed62 100644
--- a/OpenRa.Game/Traits/Activities/Harvest.cs
+++ b/OpenRa.Game/Traits/Activities/Harvest.cs
@@ -10,9 +10,10 @@ namespace OpenRa.Game.Traits.Activities
 		public IActivity NextActivity { get; set; }
 		bool isHarvesting = false;
 
-		public IActivity Tick( Actor self, Mobile mobile )
+		public IActivity Tick( Actor self )
 		{
 			var unit = self.traits.Get<Unit>();
+			var mobile = self.traits.Get<Mobile>();
 
 			if( isHarvesting ) return null;
 
@@ -57,6 +58,6 @@ namespace OpenRa.Game.Traits.Activities
 			}
 		}
 
-		public void Cancel(Actor self, Mobile mobile) { }
+		public void Cancel(Actor self) { }
 	}
 }
diff --git a/OpenRa.Game/Traits/Activities/IActivity.cs b/OpenRa.Game/Traits/Activities/IActivity.cs
index 2ec4556871..db58dfec56 100644
--- a/OpenRa.Game/Traits/Activities/IActivity.cs
+++ b/OpenRa.Game/Traits/Activities/IActivity.cs
@@ -8,7 +8,7 @@ namespace OpenRa.Game.Traits.Activities
 	interface IActivity
 	{
 		IActivity NextActivity { get; set; }
-		IActivity Tick( Actor self, Mobile mobile );
-		void Cancel( Actor self, Mobile mobile );
+		IActivity Tick( Actor self );
+		void Cancel( Actor self );
 	}
 }
diff --git a/OpenRa.Game/Traits/Activities/Move.cs b/OpenRa.Game/Traits/Activities/Move.cs
index bdbb717fb6..903e2b5629 100755
--- a/OpenRa.Game/Traits/Activities/Move.cs
+++ b/OpenRa.Game/Traits/Activities/Move.cs
@@ -49,9 +49,10 @@ namespace OpenRa.Game.Traits.Activities
 			return (u == null || u == self);
 		}
 
-		public IActivity Tick( Actor self, Mobile mobile )
+		public IActivity Tick( Actor self )
 		{
 			var unit = self.traits.Get<Unit>();
+			var mobile = self.traits.Get<Mobile>();
 
 			if( move != null )
 			{
@@ -151,6 +152,12 @@ namespace OpenRa.Game.Traits.Activities
 			return 0.5f * ( CenterOfCell( from ) + CenterOfCell( to ) );
 		}
 
+		public void Cancel( Actor self )
+		{
+			path = new List<int2>();
+			NextActivity = null;
+		}
+
 		abstract class MovePart
 		{
 			public readonly float2 from, to;
@@ -254,11 +261,5 @@ namespace OpenRa.Game.Traits.Activities
 				return null;
 			}
 		}
-
-		public void Cancel( Actor self, Mobile mobile )
-		{
-			path = new List<int2>();
-			NextActivity = null;
-		}
 	}
 }
diff --git a/OpenRa.Game/Traits/Activities/Turn.cs b/OpenRa.Game/Traits/Activities/Turn.cs
index c99b5cabf0..acfd145421 100755
--- a/OpenRa.Game/Traits/Activities/Turn.cs
+++ b/OpenRa.Game/Traits/Activities/Turn.cs
@@ -16,7 +16,7 @@ namespace OpenRa.Game.Traits.Activities
 			this.desiredFacing = desiredFacing;
 		}
 
-		public IActivity Tick( Actor self, Mobile mobile )
+		public IActivity Tick( Actor self )
 		{
 			var unit = self.traits.Get<Unit>();
 
@@ -27,7 +27,7 @@ namespace OpenRa.Game.Traits.Activities
 			return null;
 		}
 
-		public void Cancel( Actor self, Mobile mobile )
+		public void Cancel( Actor self )
 		{
 			var unit = self.traits.Get<Unit>();
 
diff --git a/OpenRa.Game/Traits/Mobile.cs b/OpenRa.Game/Traits/Mobile.cs
index 6482e0c607..cdb9b9cec8 100644
--- a/OpenRa.Game/Traits/Mobile.cs
+++ b/OpenRa.Game/Traits/Mobile.cs
@@ -53,7 +53,7 @@ namespace OpenRa.Game.Traits
 			while( nextActivity != null )
 			{
 				currentActivity = nextActivity;
-				nextActivity = nextActivity.Tick( self, this );
+				nextActivity = nextActivity.Tick( self );
 			}
 		}
 
@@ -73,7 +73,7 @@ namespace OpenRa.Game.Traits
 		public void Cancel(Actor self)
 		{
 			if (currentActivity != null)
-				currentActivity.Cancel(self, this);
+				currentActivity.Cancel(self);
 		}
 
 		public IEnumerable<int2> OccupiedCells()