Uuuuh...b-b-becaus that would make too much noise. It would wake up anyone.

[Excuse thought right then. With some luck Sigrun will believe it.

Then he voices his real reason as a mere commentary]

Besides do you seriously imagine the Kingmaker crawling through vents? I find it pretty hard to believe.

[No self-respecting masterminds would do something like moving through the ventilation system, have some style, mastermind!