Caitlyn lay there soothingly caressing Jack's head seeing his tapping the rhythm, it made her curious. What was it? She did a mental count of the taps. [I]One. Two. Three. Four.[/I] One then three quickly following it in a quick succession. She couldn't recall there ever being such a beat before, her mind trying to come up with ideas but failing. She'd ask the Doctor later about this, but after Jack went to sleep. 
"This is bad isn't it?" Rose asked knowing it was so, because of the worry on the Doctor's face. He knew enough to show that he was worried and that was never a good sign. "What do we do?" She asks.
'