When people would throw out the previous cup design, hedgehogs got their heads stuck in them searching for leftover ice cream. Hedgehogs were starving to death because they couldn't get their heads out.
The British Hedgehog Preservation Society (yes, it exists) had repeatedly campaigned for years against the cups, asking McDonald's to change the design.
Finally, in 2006, McDonald's announced that after 'significant research and testing,' they had come up with a more hedgehog-friendly design that had a smaller opening and didn't let poor Sonic die if he was a little hungry. Sadly, though, hedgehogs can't taste the deliciousness of McFlurrys anymore.