diff --git a/lesson-2/chapter-10/zombiefeeding.sol b/lesson-2/chapter-10/zombiefeeding.sol
index 109b4a1..066b83a 100644
--- a/lesson-2/chapter-10/zombiefeeding.sol
+++ b/lesson-2/chapter-10/zombiefeeding.sol
@@ -1,6 +1,6 @@
 pragma solidity ^0.4.25;
 import "./zombiefactory.sol";
-contract KittyInterface {
+interface KittyInterface {
   function getKitty(uint256 _id) external view returns (
     bool isGestating,
     bool isReady,
@@ -14,6 +14,7 @@ contract KittyInterface {
     uint256 genes
   );
 }
+
 contract ZombieFeeding is ZombieFactory {
 
   function feedAndMultiply(uint _zombieId, uint _targetDna) public {
@@ -24,4 +25,4 @@ contract ZombieFeeding is ZombieFactory {
     _createZombie("NoName", newDna);
   }
 
-}
\ No newline at end of file
+}
diff --git a/lesson-2/chapter-11/zombiefeeding.sol b/lesson-2/chapter-11/zombiefeeding.sol
index 23adcd4..e342e55 100644
--- a/lesson-2/chapter-11/zombiefeeding.sol
+++ b/lesson-2/chapter-11/zombiefeeding.sol
@@ -1,6 +1,6 @@
 pragma solidity ^0.4.25;
 import "./zombiefactory.sol";
-contract KittyInterface {
+interface KittyInterface {
   function getKitty(uint256 _id) external view returns (
     bool isGestating,
     bool isReady,
diff --git a/lesson-2/chapter-12/zombiefeeding.sol b/lesson-2/chapter-12/zombiefeeding.sol
index 737d84e..2e5e1c6 100644
--- a/lesson-2/chapter-12/zombiefeeding.sol
+++ b/lesson-2/chapter-12/zombiefeeding.sol
@@ -1,6 +1,6 @@
 pragma solidity ^0.4.25;
 import "./zombiefactory.sol";
-contract KittyInterface {
+interface KittyInterface {
   function getKitty(uint256 _id) external view returns (
     bool isGestating,
     bool isReady,
diff --git a/lesson-2/chapter-13/zombiefeeding.sol b/lesson-2/chapter-13/zombiefeeding.sol
index b2bbce5..e8fab63 100644
--- a/lesson-2/chapter-13/zombiefeeding.sol
+++ b/lesson-2/chapter-13/zombiefeeding.sol
@@ -1,6 +1,6 @@
 pragma solidity ^0.4.25;
 import "./zombiefactory.sol";
-contract KittyInterface {
+interface KittyInterface {
   function getKitty(uint256 _id) external view returns (
     bool isGestating,
     bool isReady,