Mike and Josh sarcastically singing The National Anthem.
After Josh disappears, Heather finds a bundle of twigs outside their tent. While in the movie this and its contents are horrifying, amusingly, Heather's reaction is NOPE and just chucks it away rather than open it. The actress had to be told by the crew to go back and open it. It's a very realistic reaction in a genre full of people walking into dangerous things because the movies need to get a scare in.
In the motel the night before heading into the woods, Heather shares a drink with the guys, even asking if they have any weed, apparently because she's nervous about her class project. After she takes a pull from the bottle, she shudders.
Heather: I fucking hate Scotch.
When setting up the tent for the first night, and the guys commenting on how cramped it is, Heather's reply is a loudly sarcastic "Well, I'm not usually out here with two guys, if you know what I mean!"