Monster by William Morrison - Colonizing Mars was hell, because of one thing—large, hungry critters. They flew, crawled, snarled, howled, burrowed up under the floors, chewed at doors and windows. And then, to make things worse, came the Monster...

There was a faint scratching at the door, so faint that Alice Kidd, who had been listening fearfully for precisely that sound, was at first not certain that she heard it. But, as she came close to the doorway, it was no longer possible to doubt, and a chill went through her at the thought of the creature panting eagerly on the other side. Now she could hear it whine, and, despite her knowledge that the gesture was an idle one, she could not help once more feeling the bolt behind the door. Then she made sure that the shutters too were securely barred, although these were usually in less danger; most of the animals could not apply pressure very far above the ground.

Small was staring at her, not particularly frightened, but very much interested. Her face, she thought, must be pale through the radiation tan. Ordinarily, there was nothing timid or fragile about her, or she would never have accompanied her husband to Mars; but all the same, she felt weak and helpless before the danger that threatened. And she shuddered as her five-year-old son asked, "Can it get in, Mommy?"

"I hope not, darling. Come, let's go into the other room and bolt the connecting door. And then I'll call up Daddy."

"Does it want to eat us, Mommy?"

Alice shuddered again. "Don't talk about it," she said, and carried him quickly into the next room. When the door was bolted, she pressed the contact button, asked for Mr. Kidd, and almost at once was speaking to Anthony.