diff --git a/nemubot/tools/human.py b/nemubot/tools/human.py
index a18cde2..f0e947f 100644
--- a/nemubot/tools/human.py
+++ b/nemubot/tools/human.py
@@ -57,11 +57,15 @@ def word_distance(str1, str2):
     return d[len(str1)][len(str2)]
 
 
-def guess(pattern, expect):
+def guess(pattern, expect, max_depth=0):
+    if max_depth == 0:
+         max_depth = 1 + len(pattern) / 4
+    elif max_depth <= -1:
+         max_depth = len(pattern) - max_depth
     if len(expect):
         se = sorted([(e, word_distance(pattern, e)) for e in expect], key=lambda x: x[1])
         _, m = se[0]
         for e, wd in se:
-            if wd > m or wd > 1 + len(pattern) / 4:
+            if wd > m or wd > max_depth:
                 break
             yield e