diff --git a/umbra/mistake_finder.py b/umbra/mistake_finder.py
index 8587e1bd14972ab7c37faeb5314a5f9c08b158f5..6165263553de4fbd78fcb2152c980c638028338e 100644
--- a/umbra/mistake_finder.py
+++ b/umbra/mistake_finder.py
@@ -30,6 +30,8 @@ class MistakeFinder:
         # Loop over the shadow:
         for index, word in enumerate(self._shadow):
             if not word.correct and word.mistake is None:
+                if word.word == "geen":
+                    print("boo")
                 self._determine_mistake(index, word)
         # Loop over the source:
         for word in self._source:
diff --git a/umbra/words.py b/umbra/words.py
index f65e5d7dff38a06969c70bb3c3246446e5fec2fe..6629ddb493b1f0f6ac7cf9a9f3dda24a5ca22fa9 100644
--- a/umbra/words.py
+++ b/umbra/words.py
@@ -242,6 +242,12 @@ class Sentence(list):
     def __init__(self, words):
         super().__init__(words)
 
+    def index(self, word):
+        for index in range(0, len(self)):
+            if self[index].onset == word.onset:
+                return index
+        return -1
+
     def find_previous_anchor(self, index):
         """Find the index of the last anchor before specified index.