I think you are probably referring to the
ability of some lizards to drop their tails in
self-defense against a predator and to later heal
and regrow (regenerate) the tail?
This process isn't totally understood yet, but
scientists have been able to identify a few
hundred specific genes that are activated in the
lizard's tail for regeneration. Interestingly,
humans also possess most of those same genes,
which means that with better understanding of
the lizard's regeneration process, we might be
able to advance human medicine for regeneration of
The genes control the behavior of the cells in
the lizard's tail. In an animal's body, cells
originate as stem cells, which can turn
into any kind of specific cell depending on where
in the body they are located during development.
We say that the stem cells "differentiate"
to become specific cells such as skin cells or
muscle cells, or light-sensitive cells in the eyes
or many other options. The genes in the lizard
direct the cells to "dedifferentiate," or in other
words, to be made back into something like stem
cells which can be reprogrammed to build new
tissues as needed to construct a new tail.