Animal that jumps in river with two ducks (3)
I believe the answer is:
roo
'animal that jumps' is the definition.
'in river with two ducks' is the wordplay.
'two ducks' means two replacements for 'duck'.
'in' means one lot of letters goes inside another.
'river' becomes 'r' (abbreviation for river).
'with' says to put letters next to each other.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'r'+'o'='ro'
'ro' placed around 'o' is 'ROO'.
(Other definitions for roo that I've seen before include "Jumping marsupial" , "Aussie jumper!" , "Young marsupial" , "Diminutive inhabitant of Hundred Acre Wood" , "Marsupial (abbrev.)" .)