diff --git a/sandbox/__init__.py b/sandbox/__init__.py
index 89f75ca..4562fd8 100644
--- a/sandbox/__init__.py
+++ b/sandbox/__init__.py
@@ -1,11 +1,13 @@
 from datetime import datetime
 
 
 def useful_function():
     return 42
 
 
 def is_towel_day(day=None):
+    """Return True if it's that day of the year you must not
+    forget your towel."""
     if day is None:
         day = datetime.today()
     return (day.day, day.month) == (25, 5)