I'm using MetaMask and making some changes to the [Ethereum Pet Shop][1] tutorial. I'm working with two different MetaMask accounts using the [Ganache CLI][2], and when `adopt()` is called, I'm expecting some eth to be sent back to the previous "owner", or my other account, however, it seems like no eth is being sent from the contract at all.

Here's the code:

    pragma solidity ^0.4.19;
    contract Adoption {
      address ceoAddress = 0xFc3B4137Bf7d53aB44A0FB39b31CC3F18EA6F959;
      struct Pet {
        address owner;
        uint256 price;
       
      }
    
      Pet[16] data;
    
      function Adoption() public {
        for (uint i = 0; i < 16; i++) {
         
          data[i].price = 500;
          data[i].owner = msg.sender;
        }
      }
    
      function returnEth(address oldOwner, uint256 price) public payable {
        oldOwner.transfer((price / 1000));
      }
      // Adopting a pet
      function adopt(uint petId) public payable returns (uint, uint) {
        require(petId >= 0 && petId <= 15);
        if ( data[petId].price == 0 ) {
          data[petId].price = 100;
        } else {
          data[petId].price = data[petId].price * 2;
        }
        
        require(msg.value >= data[petId].price * uint256(1));
        returnEth(data[petId].owner,  (data[petId].price / 2)); 
        data[petId].owner = msg.sender;
        return (petId, data[petId].price);
        //return value;
      }
    
    
     
      
    
      function getAdopters() external view returns (address[], uint256[]) {
        address[] memory owners = new address[](16);
        uint256[] memory prices =  new uint256[](16);
        for (uint i=0; i<16; i++) {
          owners[i] = (data[i].owner);
          prices[i] = (data[i].price);
        }
        return (owners,prices);
      }
      
    }


  [1]: http://truffleframework.com/tutorials/pet-shop
  [2]: https://github.com/trufflesuite/ganache-cli

Can anyone point me in the right direction? Thanks.

To clarify, I want to send ethereum *from* the contract to the previous "owner" of a pet.