The official says a Musudan missile or missiles have been spotted being moved out of the shed on their launchers and then being set up upright into the firing position. The missile has then been spotted by American satellites being lowered into the horizontal position and moved back into the shed. This has happened more than once.
It is part of the reason why the U.S. can't fully ascertain that there are two missiles in the shed is that only one comes out at a time. The notion that there are two is because more gear than is necessary for one missile was spotted during the transport and possibly at the current location.
"They're teasing us," said a U.S. official. This same official offered the explanation that the repeated up and down of the loader into the firing position could be training on the part of the North Koreans to prepare for a launch on short notice.