Can you imagine how two people would look after they had sex in a field in the rain? Two people who were engaged to other people. What possible explanation could they give when they returned to the house? Woody couldn't come up with an explanation, so he ignored it! And another thing, Johansson is too good looking to kill!
shareOJ disagrees with that last sentence.
shareIt was pouring, so that cleaned them after and justified their looks.
Maybe, considering how hot was Johansson and how steamy was the moment, he lasted 5 minutes, so they had no chance to really get that dirty.
Then they just zipped it up and returned to their rooms and went straight in the shower.
Also, Chris was great at improvising excuses, and Chloe was oblivious.