I understood the first, third, and fifth sentence on the first listen, except that just like jcranmer I misheard "sunny." Listened to the two remaining sentences several times, and finally decided that the second one had to be "the animal jumped in the cage of the zoo", which wasn't too far off and funnily enough persisted even after I had heard the real sample. I misunderstood the fourth completely: "<unintelligible> stayed until lunch time", but heard it clearly after listening to the correct version.

English is my second language though, I wonder if that makes any difference? For example I'd guess that compared to a native speaker, I'd have to pay more attention to the stream of sounds to determine where each word ends and the next begins. Perhaps just by expecting to hear an English sentence I automatically increased my level of attention?

I'm going to ask someone to create a few sentences in my native language to see if there's any difference, although the fact that I've now been exposed to the concept of sine-wave speech has probably in itself altered my perception of future examples.

Wow, I listened to this several months ago and I am still primed on the first sentence.

Interestingly in the first audio example of [2] I was able to understand the sentence before listening to the clear version. I've heard other examples of this phenomenon before (perhaps these exact examples on NPR?) and I recall definitely not making it out then, so maybe something was stuck in my brain the first time.

After listening only to the first one about four or five times, I made out "It was a funny day when the children were going to the park." Even after priming with the clear version, "sunny" still sounds like "funny," although the other text was much clearer.

Sine-wave speech reminds me of R2D2 from Star Wars. Does anyone know if sine-wave speech was used as an inspiration? Maybe R2D2 actually says coherent sentences in the movies, but we aren't used to that form of speech interpretation

I doubt it, only given that the sine-wave stuff I've seen is from way after the Star Wars movies. I don't think it was a concept in the 70s, but if you can find some resources, post em!