That's a line from "Museum," a Donovan song on the "Sunshine Superman" album, remembered and pointed out by commenter Kevin Walsh in the post about astrakhan, "Thinking about fetal fur."
I must have heard those lines a hundred times without having any idea I was hearing a word that would be spelled "astrakhan," so I could even get to the point of wondering what it is. It's the fur of an unborn lamb. The woman looking cool in astrakhan had told him to meet her under the whale in the natural history museum and he was sad to have to go there, so I don't think he approved of the fetal fur. And the song's refrain is "But don't do it if you don't want to/I wouldn't do a thing like that."