The researchers determined that the new tails have a single, long tube of cartilage instead of vertebrae, as in the original. Long muscles also span the length of the regenerated tail compared to shorter muscle fibers found in the original.
"These differences suggest that the regenerated tail is less flexible, as neither the cartilage tube nor the long muscle fibers would be capable of the fine movements of the original tail, with its interlocking vertebrae and short muscle fibers," Fisher said.
"The regrown tail is not simply a copy of the original, but instead is a replacement that restores some function."
The animal also has to expend quite a lot of energy to regrow the missing part. People who break off the claws on a living lobster and say, "They'll just grow back," are actually leaving that animal in a dangerous, impaired state.
On a happier note, it's still promising to know that some animals can achieve this feat in the first place. Perhaps the method could be extended to humans, once some key questions are answered.