The same three letters, in the same order, will complete the words below:

F _ _ _ R
B _ _ _ SE
D _ _ _ RE

HINTS:
#1: _ _ _ LATE could be added to the list.
#2: The missing letters make up a word in themselves
#3: The missing letters name an animal that cannot do what almost all other such animals can do.

Answer:

The letters are EMU - a flightless bird

FEMUR
BEMUSE
DEMURE
(EMULATE)