backpack on dismounting

The backpack of dismounting becomes an animate object upon the uttering of a command word. The straps will separate in half allowing the backpack to peel off you almost performing  a crab like posture and lower its self to the ground. It will also buckle and close all pockets and flaps as performing this action. This will ensure no items such as potions and vials should break when a quick cast off is needed for an unencumbered combat round or even situations such as falling into water. Better to swim than sink... when all is well you can pick the pack up again allowing the straps to magically secure them selves around you again. 

There is also a 10% chance that some of the backpacks have a anti theft device and will wrap its straps around a persons head covering their eyes and mouth if it is picked up by someone other than its owner.A strength saving throw must be made to throw it off, on failing a constitution save must be made  otherwise the thief will pass out. the pack will release its self once this happens causing no further harm. The straps may be attempted to be cut off but it will try to defend its self by flailing out causing 1 hit point damage. the pack will have a of AC 8 and 4 hit points. if the person misses the straps there is a 50 % chance of injuring the en bound person, causing half weapon damage. If the straps are cut off it will lose its securing ability until it is repaired with a creation cost of 200gp and animate object spell this should take two days to repair.  

If the backpack has not been worn for a week it requires attunement again, this will allow someone else to become the possessor . 

Notes: a command word needed to dismount from you.