Evidence

Here is a video of Simon on the porch this morning where I get him to perform some of his recently acquired tricks such as talking and clapping.

This is how he sits, although it is still rare.  He usually does it with an object in his hand, as if that helps him to forget that he's not holding on to something.

He also climbed on to the top of this little picnic table the other day.  On his way back down he lost his balance at some point and fell backwards, thunking his head, so although he tried it again today, he was a little more cautious.