Question about 1970s Cookie Monster sketch

[YellowYahooey]

I remember seeing a segment during the golden years of Sesame Street, the one where Cookie Monster decides that the smallest one among he and two Anything Muppet kids gets the cookie which the kids fight over. Cookie Monster takes advantage by mentally shrinking himself to a smaller size, and winning the cookie, thus ending the dispute.

I always wonder what made the shrinking effect possible, especially with a wall in the foreground. I wouldn't say it was the magic of blue screen technology as I saw no strange outline surrounding Cookie Monster, but is it possible that the shrinking effect was more like Cookie Monster on a skateboard or wheeled platform which moved backwards to make it looks like Cookie Monster was shrinking, and when Cookie Monster was seen putting the cookie in his mouth, I am thinking it may have been the same Muppet that would normally be used as Cousin Monster, but with a Donald Duck-style voice. Do you suppose that is likely the method used for the shrinking effect in this sketch, or what other form would it have been, other than blue screen technology?

 

[Oscarfan]

Sketch in question:

It seems clear to me that Frank is simply moving backwards, which it makes it look like he's shrinking. Then they just gave him a large cookie prop.

 

[YellowYahooey]

It seems clear to me that Frank is simply moving backwards, which it makes it look like he's shrinking. Then they just gave him a large cookie prop.

That's basically what I was thinking, though I never knew about the large cookie prop.