Nobody mentioned seeing anything and in the dark of the night, that shouldn't surprising. The Baker however, Charles Joughin mentioned hearing noises coming from within the ship of things breaking and coming apart.
As Michael said, it would have been too dark to observe any major bending from the boats. Even the break itself was mostly concealed just under the waterline, but the entirety of it was exposed when the stern settled back without the bow.
In The Daily Sketch 20 April 1912 Caroline Bonnell told how she saw that the sinking ship "was hog-backed, showing she was already breaking in two" well before she sank. She had a good view from a lifeboat.
It appears there was some kind of explosion or shudder within the ship and she began to move forwards and twist from side to side as she sank much more rapidly.
Mrs. Chaffee - Lifeboat
"The ship sank steadily until just at the last, when it plunged rapidly. Just before going down it seemed to writhe (twist), breaking into the three parts into which it was divided."
John Haggan - On the ship
"The ship was shaking very much, part of it being under water."
Miss Glynn - Lifeboat
"We watched the Titanic rolling and bobbing like a cork. All her lights were burning, and over the water we caught the strains of 'Nearer, My God, to Thee. Finally Titanic ceased rolling, seemed to hesitate a moment, and plunged her bow into the ocean."
He told a reporter - 'It was this second explosion that did the most damage. It blew away the funnels and tore a big hole in the steamer's side and caused the ship to rock as if she were an eggshell. The Titanic careened to one side and passengers making for the boats were spilled into the water.'
Lightoller - On the ship
"Finally, the ship took a dive, reeling for a moment, then plunging....The ship seemed to be heaving tremendous sighs as she went down." "She was taking a list over to port, the order was called, I think, by the chief officer. "Everyone on the starboard side to straighten her up," which I repeated....I think the ship righted. When the order was given to the passengers to go to the starboard side I am under the impression that a great many went over and the ship got a righting movement and maintained it."
"The captain was there, and he sung out: "Everyone over to the starboard side, to keep the ship up as long as possible."
"I remember somebody shouted: 'Go gently!' as if a sudden shift of weight would have disturbed the ship's position."
Frank Prentice - On the ship
"The starboard boats were swinging in the davits packed up, and until she gradually went down by the head and righted herself then we were able to get those boats away."
Frank Dymond - On the ship The stern was listing to starboard when lifeboat 15 was being filled but when it was lowered down the ship was now listing to port. It appears there was a rapid twisting motion which banged the lifeboat against the side as it was being lowered. Dymond told a reporter - 'Just as he was getting into her (lifeboat 15) something happened and he was swept on one side.' Whatever this 'something' was, it caused the starboard list to shift rapidly over to port and banged his lifeboat against the side as it was being lowered. He continued - "Our boat had been damaged by striking the ship's gunwale when we were first lowered." He described a sudden mad panic among the crowd right after that happened and how he had to fight several men out of their lifeboat as they were being lowered down rapidly. "There was a rush. Men clambered across......She was leaking on one side just about the water-level, where she had been bumped on the ship’s gunwale." This 'something' was very likely the same thing that Frank Prentice described when he said the ship "righted herself" and they were able to get the lifeboat away. This I believe would cause a twisting motion in the ship.
Alfred White - On the ship
"At twenty to two the ship seemed as if she had started again and flung us off our feet. Mr. Sloan and Mr. Parr said to me, 'Go up and see how things are going and come and tell us." He was inside the stern below decks, and it sounds like he was experiencing the same shock that threw Dymond and boat 15 against the side of the ship as the stern twisted over to port and was shunted forwards by the rapidly flooding bow.
Mr. Thayer - On the ship
"Occasionally there had been a muffled thud or deadened explosion within the ship. Now, without warning, she seemed to start forward, moving forward and into the water..."
Mr. Wennerstrom - On the ship
He was talking to the captain when he felt - "One of the boilers in the engine room exploded and threw us all apart."
The first explosive sound was heard about this time. Long before the second larger explosion.
Mr. Brice - Lifeboat
Q - How far apart in time, probably, were the two explosions?
A - From 8 to 10 minutes.
Mr. Archer - Lifeboat
"I should say they would be about 20 minutes between each explosion. From the time I heard the first one until I heard the second one it would be about 20 minutes, sir."
Quartermaster Olliver - Lifeboat
Q - Were these before or after she sank?
A - Before she sank and while she was sinking."
Q - What did you think those explosions were?
A - Myself, I thought they were like bulkheads giving in.
Charles Joughin - On the ship
"I went to the deck pantry, and while I was in there I thought I would take a drink of water, and while I was getting the drink of water I heard a kind of a crash as if something had buckled, as if part of the ship had buckled, and then I heard a rush overhead."
Q - Do you mean a rush of people?
A - Yes, a rush of people overhead on the deck.
Q - You say that you heard this sound of buckling or crackling. Was it loud; could anybody in the ship hear it?
A - You could have heard it, but you did not really know what it was. It was not an explosion or anything like that. It was like as if the iron was parting.
Q - Like the breaking of metal?
A - Yes.
Q - Was it immediately after that sound that you heard this rushing of people and saw them climbing up? A - Yes.
Mr. Thayer - On the ship
"Occasionally there had been a muffled thud or deadened explosion within the ship. Now, without warning, she seemed to start forward, moving forward and into the waterat an angle of about 15 degrees (port list?). This movement, with the water rushing up toward us was accompanied by a rumbling roar, mixed with more muffled explosions. It was like standing under a steel railway bridge while an express train passes overhead, mingled with the noise of a pressed steel factory and wholesale breakage of china." (He then slid into the water and watched the Titanic still moving forwards as she broke.) "She continued to make the same forward progress as when I left her. The water was over the base of the first funnel. The mass of people on board were surging back, always back toward the floating stern. The rumble and roar continued, with even louder distinct wrenchings and tearings of boilers and engines from their beds. Suddenly the whole superstructure of the ship appeared to split, well forward to midship, and blow or buckle upwards."