diff --git a/Day 4 lecture.md b/Day 4 lecture.md
index 5915259..40e3d63 100644
--- a/Day 4 lecture.md	
+++ b/Day 4 lecture.md	
@@ -1,6 +1,9 @@
 * Review of day 3, questions
 * Homework review
 * Reading review
+    * Execution frames
+    * Stack vs. heap
+    * Computer science stacks as a stack of cafeteria plates
     * Class/static/instance methods
     * Direct access via `__dict__`
     * Containers