Shawn was going to his dad's house for the summer, and was bringing his pet iguana Oscar (a very new pet) and didn't want Oscar to be riding down with the luggage, because hello, iguana, cold-blooded, need good climate control.
So he stuck Oscar in an empty duffel bag and decided to carry him on the plane. Like, in his lap or something.
So he went through Security with Oscar in the duffel bag, and told them, you know, to not put it through the X-Ray machine, as he was an iguana, see? The security checkpoint people being much less vigilant in those days, unlike the guards from the youth of Miles who would have disintegrated the iguana on the spot and then sifted through its remains for bombs, bugs, and the like, let Shawn, and the iguana, pass through.
Shawn got on the plane and got settled down, and then the plane was boarded by some people who did not look like they had much of a sense of humor, and they told Shawn that no, his iguana did not belong on the airplane with the passengers. In vain, Shawn argued that the iguana would be very good and would stay inside his bag. The officials said no, that he would have to check Oscar or leave him behind.
Shawn's mother, who fortunately hadn't departed the airport, was called into the negotiations, and wound up taking Oscar home with her for the summer.