diff --git a/.gitignore b/.gitignore
index 9e34881..3530b24 100644
--- a/.gitignore
+++ b/.gitignore
@@ -14,3 +14,4 @@ accumulate
 object-lifetime
 shared_ptr
 casts
+classes
diff --git a/CMakeLists.txt b/CMakeLists.txt
index abc36be..2256cd5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -14,3 +14,4 @@ add_executable(accumulate accumulate.cpp)
 add_executable(object-lifetime object-lifetime.cpp)
 add_executable(shared_ptr shared_ptr.cpp)
 add_executable(casts casts.cpp)
+add_executable(classes classes.cpp)
diff --git a/classes.cpp b/classes.cpp
new file mode 100644
index 0000000..825b257
--- /dev/null
+++ b/classes.cpp
@@ -0,0 +1,41 @@
+#include <iostream>
+#include <vector>
+
+class Animal {
+  public:
+    // Note: using *virtual* does the difference here!
+    virtual void makeSound() {
+      std::cout << "<generic animal sound>" << std::endl;
+    }
+};
+
+class Cow : public Animal {
+  public:
+    void makeSound() {
+      std::cout << "Mooh." << std::endl;
+    }
+};
+
+class Cat : public Animal {
+  public:
+    void makeSound() {
+      std::cout << "Meow?" << std::endl;
+    }
+};
+
+int main() {
+  Cat cat;
+  Cow cow;
+
+  // Does nothing:
+  std::vector<Animal> animals = { cat, cow };
+  for (auto &a: animals) {
+    a.makeSound();
+  }
+
+  // Meow? Mooh.
+  std::vector<Animal*> animalptrs = { &cat, &cow };
+  for (auto &a: animalptrs) {
+    a->makeSound();
+  }
+}