A couple took a puddle-jumping flight with 4 stops on the way to Dallas. At the first stop, a little white truck drove up to the plane's wing.

Wife: "What's that truck doing?"

Husband: "We're taking on more fuel."

The refueling process was repeated at the next two stops as well. At the last stop before Dallas:

Husband: "Ya know, in spite of all these delays, we're making pretty good time."

Wife (pointing out the window): "Maybe -- but that little white truck is keeping up with us!"