diff --git a/core/environment_test.go b/core/environment_test.go
index 01c2933..fad9f4e 100644
--- a/core/environment_test.go
+++ b/core/environment_test.go
@@ -7,7 +7,7 @@ import (
 func TestEnvironment_Mark(t *testing.T) {
 	env := NewEnvironment(3,3)
 	env.Mark(1,1,9)
-	env.Evaporate()
+	env.Evaporate(0.9)
 	for x:=0;x<3;x++ {
 		for y:=0;y<3;y++ {
 			t.Logf("mark(%d,%d) = %f", x,y,env.Sniff(x,y))
@@ -15,7 +15,7 @@ func TestEnvironment_Mark(t *testing.T) {
 	}
 
 	t.Logf("\n")
-	env.Evaporate()
+	env.Evaporate(0.9)
 	for x:=0;x<3;x++ {
 		for y:=0;y<3;y++ {
 			t.Logf("mark(%d,%d) = %f", x,y,env.Sniff(x,y))
diff --git a/core/turtle.go b/core/turtle.go
index e9c1de2..e309cc7 100644
--- a/core/turtle.go
+++ b/core/turtle.go
@@ -11,6 +11,16 @@ type Turtle struct {
 }
 
 
+type NilActor struct {
+	
+}
+
+func (NilActor) Setup(*Environment, *Turtle) {
+}
+
+func (NilActor) Run(*Environment, *Turtle) {
+}
+
 func NewTurtle(env *Environment, actor Actor) *Turtle {
 	for {
 		turtle := new(Turtle)
@@ -35,7 +45,7 @@ var headings = [][]int{{-1,-1},{0,-1},{1,-1},{1,0},{1,1},{0,1},{-1,1},{-1,0}}
 
 
 func (t *Turtle) setRandomHeading() {
-	t.heading =  rand.Intn(7)
+	t.heading =  rand.Intn(8)
 }
 
 func (t *Turtle) SetXY(x,y int) {
@@ -82,7 +92,7 @@ func (t *Turtle) FollowGradient(env *Environment, distance int, threshold float3
 	y := (t.ypos + dy)
 
 
-	h1 := (t.heading+1) % 7
+	h1 := (t.heading+1) % 8
 	dx1 := headings[h1][0] * distance
 	dy1 := headings[h1][1] * distance
 
diff --git a/core/turtle_test.go b/core/turtle_test.go
index 5838b2e..7712eef 100644
--- a/core/turtle_test.go
+++ b/core/turtle_test.go
@@ -5,7 +5,7 @@ import (
 )
 
 func TestTurtle_Wiggle(t *testing.T) {
-	turtle := NewTurtle(NewEnvironment(3,3,))
+	turtle := NewTurtle(NewEnvironment(3,3,), new(NilActor))
 	counts := []int{0,0,0,0,0,0,0,0}
 	for i:=0;i<1000;i++ {
 		turtle.Wiggle()