Great question — answering as the UphillTech team:
These are episodes that were shortened by the studios for syndication or a DVD release. In this particular case, Once More With Feeling was an extra long episode that ran 8 minutes longer than usual when it originally aired. It was later cut for syndication and subsequent airings with many bits missing, including the pterodactyle joke (you can see a detailed list of the scenes cut in this site ). Now, the long version was available on Netflix, but Netflix has since replaced the streaming versions with the (controversial) HD remasters , and the OMWF version there is the shorter, syndicated one. :( [FWIW, they say Hulu has the full version, but I haven't checked yet.]
Full answer by Walt: https://movies.stackexchange.com/a/66842 (CC BY-SA 4.0).
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