     
     var dropsPerRow = 10
     
+    func dynamicAnimatorDidPause(animator: UIDynamicAnimator) {
+        removeCompletedRow()
+    }
+    
     lazy var animator: UIDynamicAnimator = {
         let lazilyCreatedDynamicAnimator = UIDynamicAnimator(referenceView: self.gameView)
+        lazilyCreatedDynamicAnimator.delegate = self
         return lazilyCreatedDynamicAnimator
     }()
     

        
        dropitBehavior.addDrop(dropView)
    }
}

private extension CGFloat {


import UIKit

class DropitViewController: UIViewController, UIDynamicAnimatorDelegate {

    @IBAction func drop(sender: UITapGestureRecognizer) {
        drop()
