Lyre would notice that the scent of decaying flesh seems to come from the bottom of the crevasse.

Maglath: 

After the excitement of neutralizing the sentry passes, Jeb turns to John as he laments the sentry's death. Jeb says, "Remember why we are here and what the group she belonged to wished to accomplish here in Phandalin. If we can free the town and spare an innocent from having to draw blood in our eyes, then we have accomplished true good here." Jeb looks at John as he speaks to him to assist him in moving past the distaste of drawing blades on the sentry.

After reassuring John, Jeb turns to the others as he asks, "Where to lads?"

Lyre seems to be comforted by Jeb's word, but still seems unnerved at what he is doing. He also seems to stick to the wall away from the crevice. 

"I don't know.", Arikon replied to Jeb. Now that the woman was down, the situation seemed somewhat under control for the moment. "Well, we need to move forward but without a plan of this complex we are pretty much in the dark.", he shrugged. "I'll trust your intuitions."

Seeing that no one is taking the manuscript, Maglath waves it once then drops it back on the ground.

”This first bridge is a trap. It will fall.”

And then pointing to what look like clawed scratch marks on the edge of the crevasse, he adds “something may live down there. Keep your eyes open.”

Looking at the layout of the cavern they find themselves in and the different passages that lead off in different directions as well as the roof above them it seems clear they are in the basement of the manor house. It may match the outline of the building above.

”Either we check to see if something is down there, and the source of this smell or we just pick a tunnel and go.”

He nods at the one on the left, nearest them, as good a start as any.

Jeb moves to retrieve the manuscript Maglath was trying to draw attention to. Jeb will take a moment to review it. As he does so, he listens in on Maglath's note of the trapped bridge and possible chasm dweller.

Lyre will take out several of his many ball bearings and proceed to throw one in front of the staircase, another few into the chasm at a couple foot durations, and one across the chasm to see if anything pops out. He will proceed to load his crossbow and Ready a shot if any figure will emerge to inspect the bearings or the group.

Jeb picks up the paper manuscript, and sees that it is a pamphlet titled "Trampled No More," written by a person named Sanguinius Jurule. 

(History check to recognize the name. Advantage to natives of Athetome). 

It is written with clear and persuasive prose, marshalling moral and political arguments to convince the common folk to rebel against the Crown. It condemns the elf Queen, who in her long reign was supposedly responsible for many atrocities and injustices against humanity. The final line is one Jeb has heard before. 

 "The dreams of man will overthrow the tyranny of elves- down with the Crown!"

John says, "I've heard that before, back in the Night-Hollow Inn. When it gets late, people often meet in private rooms, where the pamphlet is read aloud. Curious for it to show up here."

Meanwhile, Lyre throws several ball-bearings. Nothing seems to happen to the ones thrown across the chasm or down the staircase. However, after he throws a few down the chasm, one of the bearings soars back out, clinking at the ground and landing at Lyre's feet. 

Lyre: 

Lyre's emotional struggle becomes apparent as he seems to be swayed by the pamphlet, and he begins to silently pack his gear and prepare to exit the tunnel, nervously muttering another tune, but as the ball bearing ricochets out of the abyss, Lyre will immediately turn and erratically shake his head and blink furiously as if trying to rid his head of some thought. He waves his feathered hands over to the ball bearing and points to the crevice, attempting to silently draw his attention to the ledge. He closes his eyes and warbles the sentences he heard.

Insight for Lyre to see if the intention of the voice is genuine: 7

History check for Jeb: 6

Maglath watches Lyre for a moment and notices the struggle inside the Kenku.

”They’re just words. Queen. Rebels. Lots of words. When did either care about your people or mine?” he asks.

Then he sees Lyre is distracted by something else and hears his mimicked words.

He walks to the edge of the crevasse and growls down into the dark.

”No games. Come out or we come down. You will not like that.”

History check for Murmen: 14

Murmen frowns.

"So are these bastards bandits?  Or rebels?  For rebels, they dinnae seem very worried about killin' or harmin' their own."

(Guess I'm not using my inspiration, lol.)

History 20

"Bandits, Rebels, it makes no matter.", Arikon answered. "I have my own reservations concerning the crown, but these guys were hostile towards us from the second we entered the town. A town that wasn't really happy when the Redbrands tried to establish their own rule."

Deception: 9 

Lyre seems allured by the words, but just as he is about to descend, Maglath speaks, and he reconsiders his words. 

Lyre will light a torch and throw it into the crevice that is nearest to him.

While Jeb and Arikon may have heard of Jurule's name in passing in a tavern, Murmen remembers that about half a decade ago, there was a big fuss surrounding the first humans to enter the Academy of Magic. Jurule was one of them, a prodigy mage of humble origin. Who knows what's happened to him since then?

Maglath walks over to the edge of the crevasse, which is about 20 feet deep. The bottom is concealed by shadow, and as he gazes down, the stench of decaying flesh hits him in full force. 

Then, the abyss gazes back. 

A single large, green eye blinks open at the bottom, staring back at Maglath. The goliath feels as if nails are scraping at the back of his neck, digging into the depths of his mind; as if a scalpel was attempting to pierce his mental barriers and reveal his darkest secrets. 

However, the force retreats, seeming thwarted by Maglath's mental barriers. He hears the same voice that Lyre did, a demented voice that cackles with a frenzied determination.

 Suddenly, Lyre's torch lands in the crevice. Maglath sees before him a hideous abomination made of bulbous flesh, a hunched-over figure with jagged spines protruding from it's back, with three-fingered hands that end in razor sharp talons. It has a single eye and wears the remains of old blue robes embroidered with faded arcane sigils. The creature immediately extinguishes the torch as it falls into the abyss. 

Maglath: 

Maglath almost takes a step back at the sight of the creature in the crevasse. But while unpleasant, it doesn't appear to be an immediate threat. And Maglath wants to know what information the beast claims to have.

"If you want to barter come up here," he growls down. "I will not hurt you."

Maglath makes a show of stowing his warhammer back on his belt. And then he takes a step back from the edge to make room.

Jeb observing the odd mannerisms of Maglath and Lyre in proximity of the chasm moves to check on their two newest members. As he nears he whispers, "You two ok? You seem quite distressed about our entrance into the manor."

Maglath looks over at Jeb. Then he points down into the chasm.

"There's a creature down there. It talks with its mind," he says in a normal voice. "It wants to barter. I told it to come up."

Murmen grunts.

"Strange creatures talking with their minds and offering bargains is never a good sign.  I'd stay away if I were ye."

He also offers his knowledge of Jurule to the rest of the group, although who knows how the dwarf managed to remember it better than the others.