[firebones]

So in that one, with the hand motions and the emphasis on "thread" and "well lit" and the motion across (where the Christmas lights connected the two lamps) they were implying that a thread was hanging from the Christmas lights. But since he said he "tried that" and he had to come up with something else, I assume it's some sort of front facing edifice that allowed him to circle the whole thing with a pencil (at about 85% depth) to sell it. Maybe he technically fooled them since the Christmas lights had nothing to do with it and it was something between the two lamp arms themselves.

[lisper]

I'm not going to tell you because that would be breaking the magicians code. But I will tell you this: there is a general principle of magic that the details matter. If there's something that gets your attention, like the Christmas lights, it's almost certainly there for a reason.

[crtasm]

I'm sure they had other methods in mind - the general format of the show is they have to pick which they think was used and if wrong then it's a "fool".