Peek-a-Boo Glasses can be used to see what kinds of hearts have crystallized within humans, witches, and ogres.
This is how Chocolat, Vanilla and anyone else from the magical world are able to peek at the color and presence of any hearts in range and extract them. By holding up two pairs of spread fingers to their eye(s) - it allows people from the magical world, to see the hearts in the chests of people an those hailing from Le Royaume.
- It appears that more experienced witches (or ogres) are able to view the hearts of their target without using the Peek-A-Boo glasses. Examples are Robin and Pierre.