"Girls" made its fourth season debut against the Golden Globes Sunday night (January 11), and if you weren't busy being shocked by one of the award show's many upsets (Best Animated Feature, anyone?) you were likely staring at HBO, shocked at Allison Williams' first scene of the season.

You know what we're talking about. The one where some mouth work on the part of Desi (Ebon Moss-Bachrach) made Marnie (Williams) look like this:

It's certainly not the first sex scene "Girls" has shot, but it's definitely one of the most intimate. MTV News caught up with Moss-Bachrach, whose duplicitous Desi sticks around this season, on the red carpet at the premiere for season four of "Girls."

"An acting teacher told me a long time ago that you should never take an entrance or an exit for granted," Moss-Bachrach said of his big opening scene. "You want to make, I believe in, like, big death scenes and big operatic entrances."

It's safe to say the butt-eating scene would qualify as a dramatic entrance.

And how exactly did they fake the big scene for the camera?

"It's all real!" Bachrach laughed, before continuing more seriously, "I don't know, you've gotta have a good trust with your scene partner. Allison and I really like each other. I trust her and I think maybe she had to trust me more for that particular scene, but I think she does. It's fun. It's a comedy.

As for what's ahead for Marnie and Desi this season, he said, "I think we have a lot more sex and there's some fighting, crying, making up, sex, fighting, crying. It's the cycle of life."

Sounds about right to us! We'll be watching to see how seemingly prim Marnie can shock us next.