It could be said that Sniffles started the Happy Tree Friends' long reputation of dying over and over since his influence on the past altered a situation resulting in Toothy's minor injury to one that results in almost everyone's death. (The description on the HTF website saying that "Building a time machine to change the past creates a deadly future for Sniffles!" may also be implying that too.)
In the beginning of the scene where Toothy breaks his arm in reverse, the text "Track toothy with camera" quickly flashes twice at the top right corner of the screen (this was removed from the remastered version of the episode on Mondo's website).
This is the one of two episodes in the TV series not to feature characters with any occupation of any kind. The other is I've Got You Under My Skin. Coincidentally, both episodes star Sniffles, and feature Giggles.
The YouTube thumbnail for Part 1 spoils one of Lumpy's deaths.
There are numerous notable differences between the merry-go-round scene in this episode and Spin Fun Knowin' Ya on which the scene is based.
In the original, Giggles did not have the diamond mark on her head, Toothy had two stray hairs atop his head, and Cuddles' cheeks were white at the beginning. These are fixed in the present episode.
In the original, Cuddles, Giggles, and Toothy have their mitten hands throughout the episode, while now their fingers can be seen.
In the original, Lumpy is neither paying attention to the kids nor smiling. In this episode, he is smiling at and watching the kids.
In the original, only Cuddles laughs and tells Lumpy to go faster. In this episode, all three laugh and tell Lumpy to go faster.
In this episode, Toothy flinches after Lumpy begins pushing them faster, whereas he did not do that in the original episode.
In this episode, Toothy's expression changes before he flies off the merry-go-round, whereas in the original it did not change until after.
When Toothy flies off the merry-go-round in this episode, he flies in the opposite direction than he did in Spin Fun Knowin' Ya.
In the original, Toothy's blood splatters in a design, but in this episode it makes more of a spaced out splatter.
In this episode, the pole that Giggles holds onto is hollow when it breaks off. In the previous episode, when it breaks off, it is solid.
In this episode, during Giggles' cut in half from merry-go-round, the background is a little zoomed out.
In the original, Giggles is cut completely in half by the stump. In the present episode her spinal cord remains intact.
In the original, one cannot see Giggles' teeth when she is cut in half, but they are present in this episode.
In the original, chunks of Cuddles' body can be seen coming out of the airplane's engine. In this episode, only his blood flies out.
After Toothy and Giggles fly off the merry-go-round in this episode, Cuddles yells, "Oh my god I'm gonna die, not this old death again!" whereas in Spin Fun Knowin' Ya he shouts, "Alright! Alright! I don't wanna die!"
In Spin Fun Knowin' Ya, Cuddles' hands face the wrong way at the end. In this episode, they face the right way.
In the original, when Lumpy makes the "OK" sign, he has five fingers. But when he makes it in this episode, he has four fingers.
To date, this episode marks the only time in the series Sniffles was able to eat and hold down an ant.
In total, Sniffles travels back in time seven times.
The order of the events that takes place are roughly:
Sniffles plants the trees in prehistoric times.
Sniffles chops down the trees and dismantles the playground equipment.
Lumpy, Cuddles, Giggles, and Toothy arrive at the playground.
Toothy breaks his arm or Toothy impales Lumpy or Toothy walks away from the spot the slide was in or Lumpy, Cuddles, Giggles, and Toothy find the merry-go-round.
Lumpy is impaled by the seesaw handle or Cuddles is flung into space or Cuddles is rescued by Sniffles or Toothy gets flung into a tree.
Giggles is crushed by a garbage truck or Giggles is crushed by a swing-set or Giggles hits a stump and splits in half.
Cuddles is flung into an airplane propeller.
Lumpy asks Sniffles to help him deal with Toothy's broken arm or Lumpy asks Sniffles to help him deal with the deaths of Toothy, Giggles, and Cuddles.
Sniffles knocks over his glass of milk or Sniffles is crushed by the time machine.
Sniffles begins building the time machine or Sniffles goes to help Lumpy.
The moral in this episode is the same one used in Better Off Bread. Which makes sense since both episodes involve time travelling.
This is the first episode where Sniffles has a starring role and survives. (Debatable, though it may not count, since he got crushed by his past self from the past timeline.)
This is the second time a character turns back time just to get back something that the character planned on eating/drinking. The first time is in Better Off Bread with Splendid.
The title of this episode has two possible meanings:
There's a 1999 movie with the same name.
It is also a term that means to quickly remember a previous moment in your life just by the sight of an object.
The moral means that people will eventually get over insults, injuries, and hatreds.
The movie Sniffles is watching at the start of the episode is Back to the Future, since you can see a shot of the DeLorean speeding off and leaving two fiery trails behind, one of the many iconic events of the movie.
The scene towards the end of the episode with the merry-go-round is a remake of the episode Spin Fun Knowin' Ya. In other words, Sniffles likely caused the events in the short.
When this episode aired along with Chew Said a Mouthful and See What Develops on YouTube, the alternate title for the trio of segments was "Behind the Eight Ball". Lumpy, Toothy, and Giggles appear in all three episodes. Toothy dies in all three and Giggles dies twice, while Lumpy survives in all three.