My experiences doing a quick turnaround in MIA, but departing Canada in YYZ:

"Where are you going sir"
"Miami"
"How long are you there for"
"7 hours" (Agent's 'internal red alert system immediately picks up')
"WHO are you meeting"
"No one, sir"
"What are you going to do when you're there"
"Sleep"
"Why are you doing this"
"Blah blah, lounges, status, upgrades, travel in the future"
"If we searched your bags, would we find anything suspicious"
"Absolutely not"
"Are you ABSOLUTELY sure that we wouldn't catch you with anything"
"Yes sir"
"Ok... (Laughs)"

We'll see how it goes when I apply for NEXUS in the next 2 or 3 months...