diff --git a/about_channels.go b/about_channels.go
index 2ecd01f..e183462 100644
--- a/about_channels.go
+++ b/about_channels.go
@@ -5,7 +5,7 @@ func aboutChannels() {
 
   assert(len(ch) == __int__) // channels are like buffers
 
-  ch<- "foo" // i mean, "metaphors are like similes"
+  ch <- "foo" // i mean, "metaphors are like similes"
 
   assert(len(ch) == __int__) // they can be queried for queued items
 
@@ -21,7 +21,7 @@ func aboutChannels() {
 
   assert(__delete_me__) // we'll need to make room for the queue, or suffer deadlocks
 
-  ch<- "bar" // this send will succeed
-  ch<- "quux" // there's enough room for this send too
-  ch<- "extra" // but the buffer only has two slots
+  ch <- "bar"   // this send will succeed
+  ch <- "quux"  // there's enough room for this send too
+  ch <- "extra" // but the buffer only has two slots
 }
diff --git a/about_interfaces.go b/about_interfaces.go
index ab364e3..c6d4e8a 100644
--- a/about_interfaces.go
+++ b/about_interfaces.go
@@ -1,10 +1,19 @@
 package go_koans
 
 func aboutInterfaces() {
-  mspaint := &program{3} // mspaint is a kind of *program, which is a valid 'runner'
-  runOnce(mspaint)       // runOnce takes an abstract 'runner' type
+  bob := new(human)     // bob is a kind of *human
+  rspec := new(program) // rspec is a kind of *program
 
-  assert(mspaint.runTimes == __int__) // conformed interfaces need not be declared, they are inferred
+  assert(runner(bob) == __runner__) // conformed interfaces need not be declared, they are inferred
+
+  assert(bob.milesCompleted == 0)
+  assert(rspec.executionCount == 0)
+
+  runTwice(bob)   // bob fits the profile for a 'runner'
+  runTwice(rspec) // rspec also fits the profile for a 'runner'
+
+  assert(bob.milesCompleted == __int__)   // bob is affected by running in his own unique way (probably fatigue)
+  assert(rspec.executionCount == __int__) // rspec can run completely differently than bob, thanks to interfaces
 }
 
 // abstract interface and function that requires it
@@ -13,16 +22,27 @@ type runner interface {
   run()
 }
 
-func runOnce(r runner) {
+func runTwice(r runner) {
+  r.run()
   r.run()
 }
 
 // concrete type implementing the interface
 
+type human struct {
+  milesCompleted int
+}
+
+func (self *human) run() {
+  self.milesCompleted++
+}
+
+// another concrete type implementing the interface
+
 type program struct {
-  runTimes int
+  executionCount int
 }
 
 func (self *program) run() {
-  self.runTimes++
+  self.executionCount++
 }
diff --git a/setup_koans_test.go b/setup_koans_test.go
index 6030246..8ce24b2 100644
--- a/setup_koans_test.go
+++ b/setup_koans_test.go
@@ -10,12 +10,15 @@ import (
   "testing"
 )
 
-var __string__ string = "impossibly lame value"
-var __int__ int = -1
-var __byte__ byte = 255
-var __bool__ bool = false // ugh
-var __float32__ float32 = -1.0
-var __delete_me__ bool = false
+const (
+  __string__ string = "impossibly lame value"
+  __int__ int = -1
+  __byte__ byte = 255
+  __bool__ bool = false // ugh
+  __float32__ float32 = -1.0
+  __delete_me__ bool = false
+)
+var __runner__ runner = nil
 
 func TestKoans(t *testing.T) {
   aboutNumbers()