I am trying to think of an object to put inside a box for a party. The guests have to insert their hands and g?

guess what it is...... I want something a little quirky perhaps, not food or slime as i keep finding on search engines. I thought perhaps something hanging in box or on bottom, something that seems obvious but perhaps isnt. I have wracked my brain for weeks now and am getting no where. Can anyone help ? Pretty Please. Ideas would be appreciated ................... xx