Sorting sorts & Statcking stacks

Managed to show Kimi how to sort the round peg into the sorter. Round is the easiest. He enjoys doing this now as well as stacking the Lego blocks (thanks, aunty Sherl for the pressie!). But I can't understand why he needs to open the lid of the sorter after putting 1 in? To check? Beats me!

Next will teach him how to sort the triangle... think star would be the most difficult. But, we'll get there, I'm sure!