diff --git a/lib/modesty/experiment.rb b/lib/modesty/experiment.rb
index 05351bd..c847200 100644
--- a/lib/modesty/experiment.rb
+++ b/lib/modesty/experiment.rb
@@ -5,11 +5,17 @@ class Error < StandardError; end
 
   module ExperimentMethods
     def experiments
-      @experiments ||= {}
+      @experiments ||= Hash.new do |h, k|
+        raise Experiment::Error, <<-msg.squish
+          Unrecognized experiment #{k.inspect}.
+        msg
+      end
     end
 
     def add_experiment(exp)
-      raise Error, "Experiment already defined!" if self.experiments[exp.slug]
+        raise Experiment::Error, <<-msg if self.experiments.include? exp.slug
+          Experiment #{exp.slug.inspect} already defined!
+        msg
       self.experiments[exp.slug] = exp
     end
 
@@ -38,8 +44,8 @@ def decide_identity(options)
       end
     end
 
-    def experiment(exp, options={}, &blk)
-      exp = self.experiments[exp]
+    def experiment(sym, options={}, &blk)
+      exp = self.experiments[sym]
 
       identity = decide_identity(options)
 
diff --git a/lib/modesty/metric.rb b/lib/modesty/metric.rb
index c3013bd..fca0d88 100644
--- a/lib/modesty/metric.rb
+++ b/lib/modesty/metric.rb
@@ -7,13 +7,17 @@ module MetricMethods
     attr_writer :metrics
 
     def metrics
-      @metrics ||= {}
+      @metrics ||= Hash.new do |h, k|
+        raise Metric::Error, <<-msg.squish
+          Unrecognized metric #{k.inspect}
+        msg
+      end
     end
 
     def add_metric(metric)
-      if self.metrics[metric.slug]
-        raise "Metric #{metric.slug.inspect} already defined!"
-      end
+      raise Metric::Error <<-msg if self.metrics.include? metric.slug
+        Metric #{metric.slug.inspect} already defined!
+      msg
       self.metrics[metric.slug] = metric
     end
 
@@ -26,11 +30,7 @@ def new_metric(slug, parent=nil, &block)
 
     #Tracking
     def track!(sym, *args)
-      if self.metrics.include? sym
-        self.metrics[sym].track! *args
-      else
-        raise Metric::Error, "Unrecognized metric #{sym.inspect}"
-      end
+      self.metrics[sym].track! *args
     end
   end
 
diff --git a/spec/experiment_spec.rb b/spec/experiment_spec.rb
index ab8ecb5..e928702 100644
--- a/spec/experiment_spec.rb
+++ b/spec/experiment_spec.rb
@@ -86,6 +86,12 @@
     end
   end
 
+  it "raises Modesty::Experiment::MissingError if exp is missing" do
+    lambda do
+      Modesty.group(:idontexist)
+    end.should raise_error(Modesty::Experiment::Error)
+  end
+
   it "assigns guests to :control" do
     Modesty.identify! nil
     Modesty.group(:ab_test).should == :control
diff --git a/spec/metric_spec.rb b/spec/metric_spec.rb
index e133559..5160e6f 100644
--- a/spec/metric_spec.rb
+++ b/spec/metric_spec.rb
@@ -6,7 +6,7 @@
   end
 
   before :each do
-    Modesty.metrics = {}
+    Modesty.metrics.clear
   end
 
   it "can create a metric without a block" do
@@ -47,10 +47,6 @@
     Modesty.metrics[:foo/:bar/:baz].parent.should_not == nil
     Modesty.metrics[:foo/:bar/:baz].parent.slug.should == :foo/:bar
   end
-
-  after :all do
-    Modesty.metrics = {}
-  end
 end
 
 describe Modesty::Metric, "Tracking Metrics" do
@@ -60,7 +56,7 @@
 
   before :all do
     Modesty.set_store :redis, :mock => true
-    Modesty.metrics = {}
+    Modesty.metrics.clear
     Modesty.new_metric :foo do |foo|
       foo.description "Foo"