xkcd #3098: Trojan Horse

Title text:

Ultimately, history would imperfectly record the story of the Foal of Troy.

Transcript:

[A horse is facing Cueball and Ponytail, who are standing in front of an entrance below a tower.]
[In an inset panel, Cueball is talking to Megan and Hairy.]
Cueball: When the Greeks departed, they left behind a horse as a gift.

[Hairbun is standing behind a horse, with Cueball standing in front.]
We took it as a gesture of peace, but it carried a secret payload.

[A smaller horse is standing behind the horse from previous panel, which is looking behind at it.]
One night, from within the horse, another, smaller horse emerged!

[Close-up on Cueball.]
Cueball: Our guards have been unable to determine the inner horse’s objective, but it has begun to show an interest in our oats.
Off-panel voice 1: An attack on Troy’s food supply!
Off-panel voice 2: How dare they!?

Source: https://xkcd.com/3098/

explainxkcd for #3098