Ernie buys an invisible ice cream cone..
You know, it's gotta be tough being a Sesame Street writer. On the one hand, you want to be funny; on the other hand, you don't want to set a bad example. On the one hand, you need to create conflict/tension between the characters; on the other hand, you can't create an antagonist that's too dangerous or menacing. It must be an endless balancing act. Lefty is a funny character, but it's probably just as well that you don't see him so much anymore.
A while back I was reading a satirical piece about Bert, Ernie and the proverbial elephant in the room, (a subject which I intend to address directly next month, so please hold all related comments until then), and the writer of the piece characterized Ernie as being stupid, which not only offended me but also made no sense. If Ernie were stupid, how could he be constantly putting things over on Bert or, in this case, Lefty? The whole point of Ernie's character is that he's a child proxy who's clever enough to run circles around adults; if Ernie were stupid, that would defeat the whole purpose, and then where would we be?
The thing is that Ernie, like all Muppets, is an innocent. Somewhere along the line, the word "innocent" started to be used as a synonym for "ignorant," and then became further vulgarized as a euphemism for "stupid." But as this sketch clearly shows, Ernie is not stupid. If anything, he is stupid like a fox.
There's a lot more I could say on that subject, but it will probably just end up becoming pretentious and dull (if it hasn't already) so I guess I'll stop there for now.