What can someone do with 'residue'?

I know what Comrades Hawley and Chertoff can do with all these diversions and where they can both go.

Comrade Lip Pawley, Spokeshole for the Terrorism Support Agency:

"We did not get any false positives for explosives in IAH, so we rescreened all the bags in EWR. Sooner or later, the layers of the system work."