Potty Training Tricks

We've been making passes at potty training with 2.5 year old Caleb. One of the incentives we've offered is "big boy underpants". Replete with Thomas the Tank Engine characters and bright, fun colors, you'd think they'd be a blast. But Caleb has proven to be a tough customer, and, in a show of defiance - or perhaps confusion - has misplaced his underwear...