diff --git a/lectures/21_hash_tables_II/README.md b/lectures/21_hash_tables_II/README.md
index 9a81f15..fcc1fdc 100644
--- a/lectures/21_hash_tables_II/README.md
+++ b/lectures/21_hash_tables_II/README.md
@@ -167,3 +167,4 @@ but requires more work to get right.
 - [Leetcode problem 225: Implement Stack using Queues](https://leetcode.com/problems/implement-stack-using-queues/). Solution: [p225_stack_using_queues.cpp](../../leetcode/p225_stack_using_queues.cpp).
 - [Leetcode problem 232: Implement Queue using Stacks](https://leetcode.com/problems/implement-queue-using-stacks/). Solution: [p232_queue_using_stacks.cpp](../../leetcode/p232_queue_using_stacks.cpp).
 - [Leetcode problem 102: Binary Tree Level Order Traversal](https://leetcode.com/problems/binary-tree-level-order-traversal/). Solution: [p102_level_order_traversal.cpp](../../leetcode/p102_level_order_traversal.cpp).
+- Play this [animation](https://jidongxiao.github.io/CSCI1200-DataStructures/animations/trees/level_order/index.html) to see how the level order traversal works.