Anything fine and long enough, I think. I've heard some people leave out long hairs for birds to make nests with... I mean, I've never known anyone who'd admit to that, but still, don't do it.

[He stows the little scissors and balls up the nasty bit of string. ...what's he going to say to this guy when the bird flies off. Hmm.] Yeah, go ahead. I think she wants to get back to her friends.