Black cat shows energy (6)
I believe the answer is:
bounce
'energy' is the definition.
(bounce can mean energy or liveliness)
'black cat' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'cat' becomes 'ounce' (ounce can mean a snow leopard).
'b'+'ounce'='BOUNCE'
'shows' acts as a link.
(Other definitions for bounce that I've seen before include "Spring back like a rubber ball" , "Rebound; self-confidence" , "Recoil like rubber ball" , "Rebound (of ball)" , "Reflect back from a surface" .)