Of course Peeta knows how best to calm the female morphling and ease her suffering as she dies: they both got through their games by camouflage. They're both artists. Which of course makes Peeta's line about "all those colors" even more tear-inducing.
During training, Haymich tells Katniss that: "Half the tributes want to be your allies". You'd think it's a figure of speech, but later, as they fly from the wrecked arena, he explains Plutarch's sabotage of the games - "Half the tributes agreed".
Plutarch starts giving Snow advice straight out of Machiavelli, what with the whole, it is better to be fear than loved. However, it seems he has forgotten the second part of that, which is that it is important to never be hated, for those who hate you will endure any suffering to spite you. But, considering he's a magnificent bastard whose trying to start the rebellion, it could be he has read the entire quote, and knows what exactly he is doing
There is also the firmly held belief that Machiavelli was purposely dispensing bad advice when he wrote that (as he was being forced to write it anyway) which makes it even more meaningful that Plutarch is giving this advice to Snow.
It's also implied that he's the one who suggested the Quarter Quell's motif to Snow. Which perfectly falls in line with his plans.
There's a brief moment when an older Capitol man touches Katniss's shoulder as she and Peeta walk through the crowd to Snow's mansion. Given what we know Finnick revealed in Mockingjay, there's only one way to inerpret that creepy gesture.
When laying the wire down for the electrocution trap, Johanna insists that they move quickly because she doesn't want to be anywhere near the water when it gets electrocuted. She states, "Frying is not the way I want to go". In Mockingjay, the Capitol's main method of torture for her is submerging her in water and then giving her electrical shocks. This is so effective that she becomes intensely phobic of water.
The reaped Victors from District 1 are Cashmere and Gloss, the only sibling pair to ever win the Hunger Games. They may be Careers who were willing to kill strangers in their past Games, but now they're being pitted against their own brother or sister, something they never anticipated or thought was possible under the Games' rules. The fact that they're stated to share a close and loving relationship just makes it all the worse. Even the Capitol's citizens are upset by this.
Their body language is very telling. Compared to the other Victors, Gloss and Cashmere are interviewed together by Caesar and subtly use their familial relationship to appeal and gain sympathy from the Capitol's citizens. They sit close and hold hands through the whole debacle, Gloss bluntly stating that their shared participation in the Quarter Quell isn't by choice. One is never seen without the other during training or in the arena, either.
And then they both die within seconds of each other in the Quarter Quell. The only slightly good thing about this outcome is that Gloss and Cashmere weren't forced to make the choice of having to commit fratricide or mutual suicide in the end.
It's likely that Snow himself organized their paired reaping, especially since they come from such a crowded pool of District 1 Victors. Or one of them was reaped by themselves and the other felt obligated to pull a Katniss and volunteer to fight alongside their selected sibling. This shows that not even family members are safe from having to kill each other in the Games.
Once the Cornucopia is spun, Heavensbee remarks about wanting to see how the Tributes tell time now. However, they'd already figured out that the easily visible and distinct tree that is hit by lightning (which they have no trouble identifying and finding again later) was the landmark that signified 12 o'clock. Given that they'd also mapped out several of the other wedges in relation to it, simply standing on the shores of the lake should still allow the Tributes to tell the time and direction (in relation to the hourly events), even with the Cornucopia spun.
Considering Heavensbee was secretly working against Snow the whole time, the above "mistake" was probably intentional.