Possible Clues:

• Not fixed
• See a book spy's concealed — not secure?
• Not fixed in place
• Medic, very skilled, not likely to get stuck?
• Like couches on casters
• Presumably not “stick” of furniture?
• Mobile
• See a book spy pocketed, not being secure
• Able to be conveyed from one place to another
• See sailor plugging source of leak — perhaps not fixed