Solving this puzzle involves finding names for a number of hybrid animals. The flavortext clues that the sounds of the animals’ names should be combined, rather than the letter. The precise mechanic requires attaching the first sound of the “head” animal to the sound of the “body” animal, minus any initial consonant. Each hybrid name is an existing English word which fits into the blanks given, though the spelling of the sounds may be different than in the original animals. The correct combinations are:
Narwhal + Cat = GNAT
Goat + Squirrel = GIRL
Koala + Parrot = CARROT
Wolf + Otter = WATER
Fox + Beaver = FEVER
Monkey + Puffin = MUFFIN
Bear + Sheep = BEEP
Seahorse + Eagle = SEAGULL
Walrus + Dragon = WAGON
Seal + Horse = SOURCE
Hummingbird + Mouse = HOUSE
Rabbit + Snake = RAKE
Reading down the columns, the letters in the green blanks spell out “GIRAFFE GOOSE“. Following the same rule with these two animals gives the hybrid JUICE. Note that some alternate answers are possible, but they either don’t fit the blanks (like Hummingbird + Rat = HAT) or result in the same letter being extracted (such as Bunny + Snake = BAKE).
*I am aware that GIRL and SQUIRREL do not technically rhyme, due to having a different number of syllables. However, given that most of the English-speaking world pronounces the ends of the two words virtually identically, I deemed it to be fine.