This is another thing that we see in clinical practice. We see a baby who has RDS, who is trying to ventilate him or herself, and we see these funny things called intercostals retractions, which you don't see in too many other disease processes. So why does the baby have intercostal retraction. The chest wall in a premie is compliant because the bone hasn't mineralized, it's soft. But the lung is noncompliant, because there is no surfactant. So the kid is trying to breath in, he's got stiff lungs, soft bones, he can't really do the job right, we need to wait until the lung becomes compliant and the chest wall becomes noncompliant and then we won't need retractions anymore. So that's the explanation for retraction. So, Victor, we'll ask you that tomorrow in rounds.