So I noticed after you win a battle that Red Monika puts her hand up in front of her face. At first I was wondering if she was checking her breath, but then I realized that she was smelling her fingers. She must really love the smell of that gunpowder! Kudos to the team for putting in small details that help enhance the overall experience!
I believe she is covering her mouth while she laughs at the defeat of the enemies. but i could be wrong.