Bag of "Holding"

This bag appears to be a bag of holding even under examination, how ever it is in fact a trapped bag to prevent theft.

Made of brown waxed leather, the bag can hold 20 lbs and about 1 square foot of things. When a person or creature opens the bag, they have to succeed a Wisdom saving throw of 15 or they are paralyzed for an hour. If another creature closes the bag however, they will be released from the spell.