Letter Oo!
Big O, little o!

Ostrich, Ostrich! Who is your best friend?
Ostrich! Who is your best friend?
"Ox, Ox! Ox is my best friend.
Ox! Ox is my best friend."

ostrich
ox

Ox, Ox! Who is your best friend?
Ox! Who is your best friend?
"Otter, Otter! Otter is my best friend.
Otter! Otter is my best friend."

otter
octopus

Otter, Otter! Who is your best friend?
Otter! Who is your best friend?
"Octopus, Octopus! Octopus is my best friend.
Octopus! Octopus is my best friend."

/o/ is the sound of Oo.