I think I got it...

Okay, so all I have to do is stick my foot in the hole at the top.  Wait--what are these dangle-y bits for? [sigh] Who knew shoes could be so complicated?!

He took my spot!

River is a bit jealous that Simon managed to sit in the missing shoes spot before she could.  After all, he knows that she just loves shoes and it is the best place to check out all the shoes because you're surrounded by them!
I wish I could've caught the next instant because they looked like a pair of mismatched bunny slippers as they sat side by side amongst the shoes.  I think Simon realized his error and beat feet out of there pretty quick.