Bailment vs Pledge: When do I Get My Stuff Back?

Dudes, I'm freaking out! Been studying all night and just got it - bailment and pledge are NOT the same thing! Main difference, right? Ownership doesn't pass in a bailment, but in a pledge, it does. Now, I'm on the fence about whether a bailment should be considered a "security interest" (a la Pledge, Sec 172 CPA) if the goods are in the possession of the bailor. If they've lost the goods, and they're in your possession, is it not a kind of pledge? Help me out, fellow contract law enthusiasts!

1. Do you agree with me that a bailment should be considered a security interest? 2. Provide a case example to support your point! 3. How do we differentiate between bailment and pledge when goods are lost or misplaced?