A slug, capable of crawling inside orifices

The ship landed with a great crash, throwing up a great column of water as it did. The slug, using neurolinked control, powered off all systems as it sank. The escape hatch opened with a hiss, and ocean water flooded in.

The slug was no stranger to swimming. It had infiltrated more than one water-based species before. It glided up and out of the sleek metal pod, swimming upward towards the surface while its ship sank into the inky darkness.

It was nighttime here. The slug emerged from the waters, poking its slick purple head around in the air like some sort of periscope. Lights came from the shore in the distance. Firelight? These humans were even more primitive than the slug had expected. Around the bonfire were humans, talking in some strange language the slug had not yet been able to learn. That would change as soon as it gained access to a host.

Doing so would be easy. The slug excelled in possession, sliding itself inside the orifices and openings of the host and seizing control. Its small size and slick, porous purple body capable of secreting lubricating slime allowed it to fit in almost anywhere.

As the slug silently swam further shoreward, it contemplated exactly how to approach this situation. It caught a lucky break. Two of the humans, one apparently male and one female, ran towards the water, tearing off clothing garments as they did so. As they did, the slug heard something it assumed was laughter, though it could easily be crying in the mannerisms of other species.

The slug dove underwater to lurk as the humans approached, now almost totally naked. It spotted one pair of legs diverge from the other, heading further into the deep water. Little did they know what gleefully awaited them.