Hera continues to run the light over the rack, until she finds something that looks like a row of levers. She looks over it very briefly, and then quickly grabs the lever on the far right and slams it down, before jumping out of the way.

Because the moment she pulls the lever, one of those heavy droids disconnects from the rack, and slams down to the floor where she had been standing the moment before.

Which, incidentally, is also where Thrawn has been standing, if three paces back.