Boglis Kamm and Slint, two shape-shifting aliens, arrive on Earth to scout it out as a potential planet for invasion. They disguise themselves as humans, poke around a bit, and are dismayed to discover that after breathing the polluted atmosphere of Earth they are unable to shape-shift back into Arcturan form. In human form they cannot operate their spaceship, so they are stuck on Earth for good.

Published in the August 1964 issue of Worlds of Tomorrow, and collected in Christopher Anvil's collection The Trouble with Humans from Baen.