diff --git a/README.md b/README.md
index 45d6787..07776cc 100644
--- a/README.md
+++ b/README.md
@@ -451,6 +451,9 @@ Humbug implements a basic suite of Mutators, which essentially tells us when a
 particular PHP token can be mutated, and also apply that mutation to an array
 of tokens.
 
+Note: Source code held within functions (rather than class methods) is not mutated
+at this time.
+
 Binary Arithmetic:
 
 | Original | Mutated | Original | Mutated |
diff --git a/features/bootstrap/FeatureContext.php b/features/bootstrap/FeatureContext.php
index c15b3b2..3d270ec 100644
--- a/features/bootstrap/FeatureContext.php
+++ b/features/bootstrap/FeatureContext.php
@@ -106,7 +106,7 @@ public function iShouldSee(PyStringNode $string)
      */
     public function iShouldSeeContaining(PyStringNode $string)
     {
-        if (!preg_match('/' . preg_quote((string) $string) . '/', $this->appTester->getDisplay())) {
+        if (!preg_match('/' . preg_quote((string) $string, '/') . '/', $this->appTester->getDisplay())) {
             throw new \RuntimeException(sprintf(
                 'Output did not match expected pattern:%s%s', PHP_EOL, $this->appTester->getDisplay()
             ));
diff --git a/features/running/developer_sees_mutant_error_result.feature b/features/running/developer_sees_mutant_error_result.feature
index a51782f..ce99238 100644
--- a/features/running/developer_sees_mutant_error_result.feature
+++ b/features/running/developer_sees_mutant_error_result.feature
@@ -24,7 +24,7 @@ Feature: Use Humbug
                     $foo = new Foo;
                     $r = $foo->add(2, 1);
                     // emulate error
-                    if ($r !== 3) $foo->bar();
+                    if ($r !== 3) require __DIR__ . '/this.does.not.exist.xyz'; 
                     $this->assertEquals(3, $r);
                 }
             }
diff --git a/features/version.feature b/features/version.feature
index 315ab0c..fc21ad8 100644
--- a/features/version.feature
+++ b/features/version.feature
@@ -6,7 +6,7 @@ Feature: Developer runs Humbug with --version option
     Scenario: View Humbug version
         Given I am in any directory
         When I run humbug with "--version"
-        Then I should see:
+        Then I should see output containing:
             """
              _  _            _
             | || |_  _ _ __ | |__ _  _ __ _
diff --git a/src/Mutable.php b/src/Mutable.php
index 4b9b8d8..1e20b86 100644
--- a/src/Mutable.php
+++ b/src/Mutable.php
@@ -146,7 +146,7 @@ public function generate()
             }
 
             //TODO: handle whitespace!
-            if (is_array($token) && $token[0] == T_FUNCTION) {
+            if (is_array($token) && $token[0] == T_FUNCTION && '???' !== $className) {
                 if (!isset($tokens[$index+2][1])) {
                     continue; // ignore closure
                 }