Cargo to Callisto

Four Aarnian criminals—vicious and deadly—fled silently into the Martian night; and grimly the Patrol threw out an airtight dragnet. Nothing human could have escaped ... but what's human about an Aarnian ?
Sarah emerged from the surface of the Great Canal as sleek and brown as a seal. Laughing and sputtering, she jerked her head once over each round shoulder, parting her soaked hair and revealing her face.
Try that once again! she flung at Joe.
Joe Caradac ducked her again, and Kent shouted something from the bank that wasn't quite audible over the squeals and splashes.
What? Joe held his wife's head firmly between his knees. What'd you say, Kent?
His Senior Intendant's grin widened as he cupped his hands over it to shout again:
I said—you'll drown the poor thing!
Joe grunted as Sarah cold-bloodedly located a nerve-center in his thigh and bit it. Not this thing— he released her and she bobbed up swearing in sand-coast Martian— they had to rope it out of a canal to teach it to walk!
He narrowed his grey eyes humorously and poised for the attack, but Sarah had conceded and was swimming toward the bank. The setting sun struck a series of glowing V's in her wake. Joe rubbed his tingling leg and followed. They reached the green slope at the same time and big Kent handed them up with ease.
Ray's watching the franks, he said, and I've been watching Ray and I think we'd better get up there or he won't be able to hold off much longer. His inner man is showing through.
The pianist's dark, saturnine face peered at them over the fire as they came up and he rose, wiping his hands carelessly on his sport tunic. He had evidently gone into the canal-skimmer and changed out of his bathing suit.
How do, he greeted dourly; the damned thing itched so I took it off.