What’s missing?

What’s missing?
Article number: E523300
Where to buy this product?

One item is missing, can you find out what? Choose a theme board and matching assignment strip. Try to find the 3 items that are both on the theme board and the assignment strip. Learn to distinguish details and pick out key points. The assignment strips have an increase in degree of difficulty. Self-checking.

4 plastic theme boards
24 plastic assignment strips
wooden box