The caterpillar mystery

Arriving home this afternoon after two days at the Jersey Shore (no Glossy Ibis sighting, but a magnificent Great Egret), I spied an Eastern tiger swallowtail butterfly in my garden. Wanting to photograph it for Sophie, I grabbed my camera and quietly walked toward the butterfly, took some pictures, and returned to help Linda unload the car. On my second trip into the house, she said, "Look--what's that on the kitchen floor?" Not quite believing my first impression, I knelt down to confirm that it was a Monarch butterfly caterpillar(Danaus plexippus)--right there on our kitchen floor! How it got there, I don't know, except that perhaps it "hitched" a ride on me when I was in the garden??
Perhaps our friend, "Sue the Science Educator" knows--I just left a message on her phone--"Hey Sue, how did a Monarch buttefly caterpillar get on our kitchen floor?" (click on image to enlarge)