I knew her milkshake would bring all the boys to the yard

Maybe the excessive moaning was to bullshit him to an ego boost. :)

All of these puns are udderly ridiculous.

Could be worse, she could be yelping like a dog.

Yeah that's right, milk all the cow puns for all they're worth.

Should have played "ol Mcdonald had a farm" on the loud speaker. Maybe next time the cheapo will spring for a hotel room.

Ba-dum ts.

...and OP sat there, listening to the moo sounds... Weird, yes?

A hypothesis: Perhaps OP's sister was trying to moan heavily while her partner's... "member" was jamming her throat... restricting the appropriate airflow needed to produce true moaning sounds, and instead releasing half-moans sounding akin to that of a cow's mooing.

Or just as likely they were playing Farmville and OP mistook the **** on his computer for their bed shaking

I sincerely apologize for disgusting everyone with my hypothesis.

Lmfao! best comment i've ever read, for that sir, I thank you.

That's a little extreme, don't you think..

Oh, it'd be fun if anyone who knew you in person read your comment. They could plaster your life with pictures of cows. In your car, in your mailbox, and real cows on car rides... "Hey look, it's a cow!" -- "Hehehe, a cow, hehehe!" ... ;)

Is mooing any better?

I think I would prefer the sound of a cow mooing to a woman screeching due to an ******. .-. Hey, that might just be me though!

Well that solved the mystery of the first person to discover that a cow lactating can also be nutritious....

Yes, I'd prefer mooing to screaming. Then I don't have to assume bloody murder every time the neighbors get a little too eager.

Why on earth would he be jealous

Cuz his sister is getting some and his not.

Because op's a she.