The plural of goose is geese. A girl goose is a goose. A boy goose is a gander.
The name comes from the Proto-Indo-European root word ghans. I'm going to cut and paste a paragraph about the name origin directly from Wikipedia because it's a neat example of a commonality between bunch of exceptionally disparate languages. I often have a hard time wrapping my brain around the fact that all these languages can be related, and this example helps:
In Germanic languages, the root gave Old English gōs with the plural gēs and gandra (becoming Modern English goose, geese, and gander, respectively), New High German Gans, Gänse, and Ganter and Old Norse gās. This term also gave Lithuanian žąsìs, Irish gé (swan, from Old Irish géiss), Latin anser, Greek chēn, Albanian gatë (heron), Sanskrit hamsá, Avestan zāō, Polish gęś, Russian гусь, Czech husa, Slovak hus, and Persian ghāz.
Right? Holy bananas. Geese are foul-tempered things (pun only sort of intended) that would, I assure you, bite your eyes out given the opportunity. My high school had lots of them, and during hatching season, things could get ugly. "Geese in my way" was a legit excuse for being late to class. Except when you used it every day.
The plural of moose is moose. A boy moose is a bull and a girl moose is a cow. Which is silly, because everyone knows a cow is a cow and not a moose. Side by side comparison. C'mon. The scientific name for moose is Alces alces, from the Latin for Elk. Because in England, moose are elk and elk are... something else. I don't know what name the English have for the thing we call an elk, but given that Elk are native to a small part of the US and Asia, far away from England, I suppose it's possible the English have never heard of elk. Unlikely, but possible. Come to think of it, I don't know what name the English have for what we call pudding. Maybe they've never heard of pudding.
Moose is a native American word, meaning moose.
Holy crap, these things are cute. Don't you just want to take the little guy home? I bet he'd cuddle with you all night, and then take care of your snake problem. Because they're awesome like that. Way better than stupid cats that puke on everything you love and wake you up in the morning by biting your elbows. *Glares at sleeping cat. Then bites sleeping cat's elbow.*
The plural of mongoose is mongooses. I'm not sure what a boy mongoose is called, although more than one online resource claims that girl mongooses are called teriyaki biscuit. Let's have a hand for the Internet.
There are actually 30 some species of critters called mongooses, all members of the family herpestidae, which sounds like a disease I recently had. Mongoose comes from an Indian word, mangus, and is etymologically unrelated to goose. Say etymologically out loud. You'll thank me later.