Can somebody please explain this Gravity Falls gif pls.

[Dragonoid.Slayer]

I see this gif so often, and don't understand..
What the hell did this come from, and why is it posted so often.

[Ad Bot]

[Ipquarx]

it's r34 made by some creep creep
seriously they're like 12

[Mister Cheese]

it's r34 made by some creep creep
seriously they're like 12

basically this

[Foxscotch]

the girl bites the one of the boy's nipples, and it hurts him. later, the boy bites one of the girl's nipples as revenge, but to his surprise she enjoys it. then they stand awkwardly next to each other, facing in opposite directions, and the boy says that it isn't fair that it hurts him, but not her

[Rally]

they're siblings(? - related though), which is why it's weird

[Swollow]

theyre like 12 and are both siblings

[Satan From Wreck-It-Ralph]

theyre twins, to be specific.

[bestguy22]

the girl bites the one of the boy's nipples, and it hurts him. later, the boy bites one of the girl's nipples as revenge, but to his surprise she enjoys it. then they stand awkwardly next to each other, facing in opposite directions, and the boy says that it isn't fair that it hurts him, but not her

[The Resonte!]

i think there was a wip of it in color

[Dragonoid.Slayer]

it's r34 made by some creep creep
seriously they're like 12

w
why

[Afraidanna]

i like the guys face after his nipple gets eaten off

[Steve5451²]

it's r34 made by some creep creep
seriously they're like 12

idk man she looks pretty old in this

[Electrk.]

goddamn it not again

[Ragequit]

y'all some pussies

[kahnuu]

y'all some pussies

ya seriously