The adventurers made their way deeper under the ground, the way ahead lit only by the magical torches that they carried. The human wore scale mail and bore a round, wooden shield in his other hand. The elf wore studded leather, and carried a longbow. They grew thirsty, as their water had run out the previous day, and they had been unable to find any water along the way.
Their journey through the underdark had led through tunnels wide and narrow, high and low, winding and straight. This area happened to be very tall, and wide enough for an entire party to walk abreast with room to spare. They reached a turn, to the right, and hadn't gone far when the elf spotted what appeared to be a pool of water ahead, with several high rocks around it. When they approached, the elf suddenly dropped his eternal torch and knocked an arrow.
"What are you doing?" asked the man.
"I'm making sure that my hand's free in case I need to shoot something. What does it look like I'm doing?"
"Well, why are you doing that now, of all times?"
"I just botched a Perception roll, that's why. I don't know how useful this will be, though. Since we're without a Rogue, it's probably a trap."
"Am I to understand that you're readying your weapon on the grounds that you didn't see anything?"
"Well, if we take it slow, then I might get another roll, and maybe I can act during the surprise round."
"Do you have any idea how stupid this sounds?"
"Hey, better safe than sorry."
"OK, fine," said the man, tossing his torch down near the pool and pulling out his longsword. "Here. We'll take it in turns. You go fill your waterskin while I cover you."
Begrudgingly, the elf put away his arrow, picked up his own torch, and made his way toward the pool, his companion at his side every step of the way. He knelt by the pool and placed his bow and torch down on either side of him, specifying that each was within arm's reach. He was about to dip his waterskin in when he stopped.
"Wait, we're in the underdark. What if the water's poisoned?"
"Isn't there some kind of roll that you can make to taste-test it?"
"Why should I have to do it?"
"Because you're the Ranger! Here, if it makes you feel better, I'll swing my sword around in front of me, just in case someone's invisible and adjacent. Just hurry up."
"Yeah, alright...." With that, he scooped a handful of the liquid out of the pool and tasted it as he knelt.
With that, the transparent ooze rose out of the small pit, swallowing him whole.
The human turned around to see what had happened. "HAH!" he said, "Nice."
And then they rolled Initiative.