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By Chris Kennedy, Michele Pratusevich, and Helena Wang
Answer: HORSES

First, solve the barred crossword using the clues:

G O P P E R S G O D F R O S T
U B A H N I H A P A U A R T E
N E R D J O R G E H S E G A L
A S A L O T U S C L I M A T E
M E D A Y S G O B I O O N U S
E L O I H O S T S A N T H E M
B O X C A R S B O U T E E G S
A C H E R B L I S S A L E R T
S H I P P O P O P A M I G O S
O D E S S A E T A G E S E G A
Y O K O H L A S H E M I N O R
A N I M A L S P E T I T T I S
H A V O C O O P I U M S I L O
A T A T K U U D D R E U L E R
B E S T S T R E I N D R E R E

The crossword grid contains a number of letters that are trapped “between bars”. As suggested by the flavor text (“Release your inner animal!”), each of these trapped letters can be changed to spell the name of an animal. There are eight total (as explicitly clued by 73 Across), and are highlighted here:

G O P P E R S G O D F R O S T
U B A H N I H A P A U A R T E
N E R D J O R G E H S E G A L
A S A L O T U S C L I M A T E
M E D A Y S G O B I O O N U S
E L O I H O S T S A N T H E M
B O X C A R S B O U T E E G S
A C H E R B L I S S A L E R T
S H I P P O P O P A M I G O S
O D E S S A E T A G E S E G A
Y O K O H L A S H E M I N O R
A N I M A L S P E T I T T I S
H A V O C O O P I U M S I L O
A T A T K U U D D R E U L E R
B E S T S T R E I N D R E R E

Each of the eight locations on the grid provides 2 letters:

Grid text Animal From To
GOPPERS GOPHERS P H
GEHSE GEESE H E
BIOON BISON O S
CARSBOU CARIBOU S I
HIPPOPOPAMI HIPPOPOTAMI P T
KOHLAS KOALAS H A
OCOOPI OCTOPI O T
REINDRER REINDEER R E

This yields two words, which fit into the blanks provided under the crossword:

P H O S P H O R | H E S I T A T E

There’s another animal trapped in the bar. Applying the mechanic one more time yields the animal HORSES, which is the answer.