Fish Hook
if hook look at the design of a fish hook, you will notice the end of the hook has a barb facing the opposite direction. When used on a fish, the big hook actually catches the fish, but the barb keeps the fish from slipping off the hook. This same design can be used with LEGO robot attachment as well by simply building a big hook with some kind of LEGO element on the tip that will keep anything the hook catches from slipping back off. Again, don't over think the design; just add a simple bushing or pin on the end of your hook so that the newly captured object isn't allowed to fall off hook before you return to base with your prize e