Female Monster Surprise

Donkey: You're... A GIRL-DRAGON?

—Shrek

Ahh! A monster! A squicky mess of tentacles and seventeen eyes, a-and hideous teeth a-and his breath smells like sulfur and he opens his mouth! He's about to speak! He says:

"I'm a lady, I'll have you know."

You see, in the mind of the audience (or at least in the mind of some characters) monsters are often initially assumed to be male. Female Monster Surprise covers situations when these characters are surprised to find out that the monster is, in fact, a female.

This takes the form of a monster in some way having her gender revealed, and someone acting surprised by this.

Examples of Female Monster Surprise include:

Anime and Manga

Inverted in Slayers - A female-looking firebreather is revealed to be a "drag"-on despite Tertiary Sexual Characteristics, when Gourry gets a good glimpse of the underside.
- A chapter of Naruto did pretty much the same thing with a giant armadillo whose gender Naruto and Killer Bee argued about trying to discover, except that we ALL got a good look at its underside.
Combined with Samus Is a Girl in Mahou Sensei Negima: unlike most examples the Bounty Hunter with the Naughty Tentacles actually was a Cute Monster Girl, and it turned out the tentacles and stocky build were from a set of Powered Armor she wore.

Comic Books

In Popeye's "Plunder Island" arc, Wimpy is at one point dragged off of Popeye's ship and onto the Sea Hag by the monstrous Goon. Soaked from being in the ocean, Wimpy decides to take off his clothes while being held captive with the Goon watching him. Just as he's about to strip naked, a voice comes through the door, saying, "Keep a close eye on him, Alice." Wimpy quickly realizes who 'Alice' is, and quickly re-clothes himself, saying, "I didn't know there was a female present."

Film

In Shrek, Donkey is confronted by a dragon on a collapsing walkway and attempts to smooth-talk his way out, before realizing that the dragon is female, and she thinks that he's hitting on her.
Everyone assumes that Kevin is a boy bird in Up.
- Not unjustifiably—with many bird species the colorfully-feathered one is the male. (Peacocks are the classic example.) Kevin's plumage is modeled on a (sadly recently deceased) male Himalayan monal from the Sacramento Zoo.

Literature

In Eragon, Eragon comes with a long list of names to suggest for his newfound dragon to call her. He lists quite a few, before figuring out that the dragon is female, and he'd only suggested male names thus far.
- Another instance is seen in Brisingr with the Ra'zac. One is revealed to be female, while the gender of the other is left ambiguous.
In Guards! Guards!, the dragon tormenting the city is revealed at the last minute to be female, to the surprise of the city watch.
In Harry Potter, Norbert the Norwegian Ridgeback is in the last novel revealed to be a Norberta, to Hagrid's bafflement. According to Bill, the easiest way to tell this is that female dragons are even more vicious.
The title character in IT is protecting Its eggs, which will assumedly hatch into Mind Screw monsters just like her.
happens in Animorphs with the first free Hork-Bajir. "you mean there's such a thing as a female Hork-Bajir?"

Live-Action TV

In Reaper Nina starts giving Ben some compliments that perturb him coming from her rather masculine seeming demonic form. The later start dating, though mostly in her human form.
Lorne's mother in Angel was played by an extremely muscular, bearded man. Angel is comically baffled when Lorne goes, "Hi, Mom".
The Horta in the Star Trek: The Original Series episode "The Devil in the Dark" turns out to be female...and the "silicon nodules" that miners on its planet are destroying turn out to be her eggs.

Video Games

The dragon Hooktail in Paper Mario: The Thousand-Year Door. Despite the character being the first major boss of the story, you don't learn this until towards the end of the game.
Psychonauts - Raz discovers that the lungfish residing at the bottom of the lake is actually "Linda". Although with the deep, booming voice, the audience can be forgiven for its assumption.
Shale the golem in Dragon Age: Origins. Technically genderless in its current form, but it used to be a female dwarf.
Disgaea: Hour of Darkness: You know the Level 300-ish dragon that hangs around Laharl's throne room and helps save your ass once? She'll have you know that she's one of the more attractive of her lot.
- Dark Hero Days features a lesser surprise in the form of Actress, a female Entei. It would've been more surprising if not for the fact that you can hear her obviously female voice in the battle that occurs prior to someone bringing up her gender.

Web Comics

Hanna Is Not a Boy's Name has a vampire bat who Hanna wrongly assumes is male, and he seems to get more apologetic than she got offended when she corrects him. She has Tertiary Sexual Characteristics upon closer inspection.

Web Original

Dodoria in Dragon Ball Abridged. Vegeta is so disgusted he vaporizes her just to repress the memory (her proposal didn't help).

Western Animation

Subverted/Inverted with Bigfoot in The Venture Brothers who Steve ~~Austin~~ Summers was in love with. After Brock shaves Bigfoot for the sake of a disguise, he reveals to the audience that he's actually male.

Steve: What are you, shy? Sasquatch doesn't have anything you haven't seen before.
Brock: Sasquatch is something I haven't seen before!

Cammie in The Marvelous Misadventures of Flapjack.
The Grim Adventures of Billy & Mandy. The show itself seems to have a hard time concluding whether Jeff is a male giant spider or a female giant spider as he has been shown to lay thousands of eggs in two episodes but has a masculine voice and married the Spider Queen Velma Green. Lampshadeed by Billy.