He felt a slight sensation as something else emerged from the device and slid down his esophagus toward his stomach.

They were apparently probing him, maybe with a camera, as he could see out of the corner of his eye a screen with a moving picture of what he imagined a camera would see if it went down a throat. He watched as best as he could, seeing how the picture changed as the camera reached his stomach. They looked around for a while, then withdrew it. Then he felt something wet and slick applied to his asshole. He flinched as something else warm touched him there, knowing what was coming next. Yes, it was being eased past his sphincter, the same device. He felt it slide in about 2 or 3 inches, resting bluntly against his prostate. A brief sensation of motion was all he felt, but he knew the camera was sneaking a peek at his intestines. But as they continued the probe, they had to constantly re-position the sheath. This wasn't a straight-shot tube like the throat, but a winding trail. With each adjustment, the sheath nudged his prostate. And his dick began responding involuntarily. And this cause/effect was not missed by the tallest alien. It whispered something, and the alien controlling the camera stepped aside as the big one took control.

It no longer seemed to care about the view-screen. It was watching with all eight eyes the growing flesh of David's cock.