They will let you know if one or the other gets hurt...Peanut and Lexie play fight all the time, one time when I just got her, she was 4 months, they were playing tug of war, her bottom baby tooth came out, Peanut didn't do anything to her it just happen, Lexie pouted for 20 min...she thought Peanut had hurt her, you would have thought someone shot her they why she acted, then she was over it...