To fully understand the sheer terrifying-ness of this terror, I recommend watching a few clips from the MST3K version of The Creeping Terror.
Tegan had to admit it, the Doctor had landed them in a perfect spot this time. Sure, it still wasn't Heathrow, but for once she didn't complain about the location- a sunny meadow right next to a huge, clear lake. The weather was perfect for a day of swimming and picnicking, which was exactly what they did. It was nice, she thought as she sunned herself on a fold-out lounger, having a proper holiday.
Beside her, Nyssa picked up a towel for her hair, having just come out of the lake. "Don't you want to swim some more?"
"I just ate. Can't go in for another hour or I'll get cramps."
"No you won't. Look, Adric's all right..."
A short distance away, the Doctor wandered around the meadow. (He was the only one not in a swimming costume.) He'd been strolling around since they'd finished lunch, and was now coming back to their picnic site. "I wonder..." he began, "how long do you suppose that's been lurking there?"
"What's been where?"
A loud, blood-curdling roar rang out across the land, and the girls sprang to their feet and looked. There, emerging from the trees on one side of the clearing was a hulking beast about the size of a car. It looked like a great slug covered in matted carpet-like fur. The front end of it stood upright, like a humanoid, but without any identifiable arms or legs. Instead, it had nasty fins all over its blobby skin, and where a head should have gone were a dozen stalk eyes growing out of another mess of fur. Horrifyingly set into its front was what could only be described as an orifice- as if somebody had just skipped putting a mouth on it and went straight to the throat.
It roared again and began lumbering toward them.
"What is that?!" shouted Adric as he ran up to join them.
"I don't know," said the Doctor, "but I don't think we ought to stick around and find out."
Frozen in awe, they watched it make its way through the trees, their muscles tensed to run. A heavy silence fell over the meadow as if nature itself could sense death in the air. "...Do you think it's coming to attack us?" asked Nyssa. A few more seconds went by, and the monster was still trying to clear the tree line. It roared a third time for good measure, viciously waving its eyestalks.
"It doesn't seem to be in any hurry," Tegan remarked.
A full minute went by as they stood there awkwardly, trying to determine how to react. The Doctor checked his watch. "Well, we should probably get a move on. No sense leaving a mess behind." They began packing up the picnic things, occasionally checking on the monster's progress. It moved like a pantomime horse with too many people inside. The front half did a fearsome mix of shuffling and waddling, rocking its top back and forth like it was in a heavy wind. The back half did its level best to follow along.
At a leisurely yet wary pace, they folded up the lawn chairs, shook out the towels and tablecloth, packed up the food and dishes, deflated the pool toys and stowed them away in the beach bag, and democratically resolved the issue of who got the last slice of pie. There wasn't a moment to spare- by the time they'd finished and begun walking to safety, the monster was halfway to them. By now, it was close enough they could see two of its fins reaching out for them.
Barely ten feet into their escape, Tegan stopped and hopped in place on one leg. "Ouch!"
"What's the matter?" asked the Doctor.
"Sticker. There's stickers in the grass." She set down the beach bag to carefully pull out the offending burr and put her sandals on. The monster shuffled diabolically along and growled as she hurried for a few feet to catch up with the others.
Nyssa stumbled and dropped the lawn chairs and Adric stopped to help pick them up. Behind them, the monster waddled closer, coming dangerously close to sort of near them. It was a perilous twenty feet away when they finished gathering the chairs and strolled on.
Despite the eventual danger, curiosity soon got the best of the Doctor. "Hang on, I want to see something," he said. He stopped suddenly and began walking back toward the creature. The others followed and together they circled the beast, which tried to swing around and chase them. It had all the agility of five blind men under a heavy tarp trying to move as one, and had barely made a quarter turn by the time the Doctor came back around to the front.
"I thought we were trying to get away from it. What are you doing?" asked Tegan.
Before the Doctor could respond, the head of the beast bent at the middle, knocking the Doctor against it. His companions cried out in surprise. "No, no, no, it's okay! Look, it just wanted a hug!" The top half of the head-slash-neck halfheartedly wrapped around him. "How about that? All that walking away for noth-oh...wait...no. No, it's eating me. Give me a hand, won't you?" The flippers closest to the beast's mouth flapped weakly, trying to draw the Doctor's leg further in. He stood on the other one patiently while his friends shuffled their things around to get a free hand and pull him loose.
"Are you all right?" Nyssa asked as he brushed off his trousers and picked up the towels he'd dropped. Beside them, the beast growled in irritation and flapped its fins at them some more.
"Right as rain. It doesn't seem to have any teeth. But at least we know for sure what it wants."
Relentlessly, the beast continued its determined shuffle, speeding up to walking pace. "What is that thing, anyway?" Tegan wondered.
"It's not a relative of yours?" asked Adric. He ducked the pool noodle she swung at him.
Nyssa walked backward to get a better look at it. "It's a good question. No teeth, no arms or legs, no claws...I assume it's carnivorous if it was trying to eat the Doctor, but that just raises more questions about what it eats and how it subdues its prey."
Tegan snorted. "The only way that thing's going to eat anybody is if they volunteer!"
"Maybe there's something on this planet that moves slower?" offered Adric. They were now pausing to consider the beast pursuing them, periodically stepping backward to keep out of range.
"I was going to say it might be a scavenger, but then it shouldn't be attacking us," said Nyssa.
"Could be somebody's pet," the Doctor remarked. "Somebody with a taste for exotic animals. Or it was genetically engineered..."
"Who'd want a pet like that?" Tegan wondered.
As the chase intensified, the conversation turned from biological abominations to comments about the scenery and interesting cloud formations, rudely interrupted by voracious growls and shrieks from the beast. They made it back to the TARDIS in the nick of time, with barely a half-hour to spare. Once they dematerialised, the creature stopped and let out an ear-splitting scream of frustration at the meal that got away. Never before had it encountered prey clever enough to flee.
No matter. The town's mid-afternoon dance was in full swing. It would feed soon...