“There were no bathrooms in the tunnel,” Patrick John Flueger recalls.

Warning: This article contains spoilers for the Feb. 22 episode ofChicago P.D.

First, a car backfiring caused a panic attack at home.

Marina Squerciati as Kim Burgess and Tireni Oyenusi as Jamie Bagley on ‘Chicago P.D.'

Marina Squerciati as Kim Burgess and Tireni Oyenusi as Jamie Bagley on ‘Chicago P.D.'.Lori Allen/NBC

The big episode was one that Squerciati didn’t have a ton of time to prepare for.

“Without the words, you’re able to’t really track the journey.”

“It was insane.”

Patrick John Flueger as Adam Ruzek on ‘Chicago P.D.'

Patrick John Flueger as Adam Ruzek on ‘Chicago P.D.'.Lori Allen/NBC

One of the guest stars, no joke, used a coffee cup."

The difficult scenes didn’t end there for Squerciati, who spent some of the episode in a well.

“I was in a pool for 12 hours,” she says.

So there’s no way to get me to the top to shoot me dry.

So I only got one take of that."

Thankfully, 200 episodes in, one take was all she needed.