* Ever notice that there's something strange about Helga but you just can't pinpoint it? Could it be that Helga has only one, huge, eyebrow?
* For that matter, Helga, Harold (who also has just one), Stinky (whose are well above his eyes), and Gerald seem to be the only kids that have any eyebrows (although Rhonda's hair may hide hers - Sid removes his hat in "Heat", and Iggy removes his glasses in "Downtown As Fruits", and neither has eyebrows)
* The city name is never mentioned, although it is supposed to resemble parts of Portland, Oregon and Seattle, Washington, and there is some definite resemblance to New York City (there's a bridge that looks like the Brooklyn Bridge and a school named "P.S. (Public School) 118", which is in Queens)
* P.S. 118 was founded in 1932
* Nobody ever seems to change clothes, except for certain specific things (for example, Arnold wears his pajamas to bed, and he wears a basketball uniform when he plays for his Youth League team), just like pretty much every other cartoon out there (quick, when was the last time Bart Simpson went to school without either his red shirt or his blue shorts, and how many times has Chuckie on Rugrats been without his shirt that has Saturn on it? At least on Rocko's Modern Life, Rocko has more than one shirt, but they all happen to be the same pattern...)
* In the "Nicksclusives", there are some scenes shown where some of the characters are wearing slightly different clothes; Arnold is wearing an orange sweater over a blue shirt, and Helga's dress is all pink (including the sleeves) except for a white collar (this is what she wears in the original shorts); presumably, these are from the original version of "24 Hours to Live", which was shown in theaters with Harriet the Spy
* The back of the brim of Arnold's hat usually matches the curve of his head
* Speaking of hats, Arnold is supposed to be the one "associated" with wearing a hat, yet he removes his more often than Sid does (and just what is that round yellow thing in Phoebe's hair, anyway - it looks like a hat until you look at it close-up and notice that her hair goes through it)
I've been told by a number of people that it's called a "scrunchie"
* Helga's hair ribbon isn't tied to her hair, but is "pre-tied" and she connects it to her hair with some sort of elastic band (you can see it when Olga plays the piano in "Olga Comes Home", and she removes it without untying it in "Helga's Makeover") - note that it changes to a "tied" ribbon in later seasons (for example, in "Summer Love" and "Beaned")
* If you think you've seen Arnold and Gerald's handshake (the one where they tap thumbs) before, maybe you remember one of the older episodes of The Flintstones where Fred and one of his old friends did the same thing
* Although most (if not all) episodes have a "Music by Jim Lang" credit, nobody gets any credit at the end of the show for writing the theme song
* Not the message you want to send to young girls: except for Phoebe and Nadine, all of the "regular" girls appear to be tall and thin (of course, standing next to Arnold and Harold, everyone looks a little tall and thin)
* Depending on the episode, Arnold uses one of three different alarm clocks:
o "Arnold's Hat", "Heat", "The List", "Mugged" - an "old-fashioned" alarm clock with a miniature Arnold on top with an alarm that says "Hey Arnold" over and over (and usually it's "potato-powered"; in "Mugged", the alarm is just a bell)
o "Snow" - a clock-radio with the radio alarm set
o "The Little Pink Book" - the clock-radio with the buzzer alarm set
o "24 Hours To Live" - a clock-radio with non-electronic digits; both the buzzer and radio go off at the same time
(The digital clock-radio also "appears" in some other episodes, such as "Abner Come Home", but the above episodes are the only ones where the alarm goes off)
* From the outside, it appears that Arnold's room is on the second floor of the boarding house, but he has to climb stairs from the second floor in order to get to his room
* There's no overcrowding at P.S. 118; there are only 12 desks in Miss Slovak's classroom (except in "The List", where there appear to be 16), although not only do the students tend to change seats (Helga sits in the back in "The Little Pink Book" but in the front in "Helga's Makeover"), but the twelve students tend to change (Phoebe is in the class in "Spelling Bee" and Sheena is in "Helga's Makeover", but neither is in the class in "Tutoring Torvald" or "Olga Comes Home"); in fact, the layout changes between three rows of four (for example, in "Olga Comes Home") and four rows of three (for example, in "Helga's Makeover")
* The radio station Arnold listens to is MJZZ ("M-Jazz"), but those can't be its actual call letters as only stations in Great Britain and Northern Ireland can begin with "M"; regular stations in the USA begin with a K or a W (the "unwritten rule" is: stations west of the Mississippi River begin with K, and stations east of there begin with W)
* ...and although plenty of radio stations have jazz programs, the only remaining all-jazz radio stations in the USA (the last time I looked) are on television shows: MJZZ and The Simpsons' KJAZZ (there was a real all-jazz station KJAZ, but it changed formats a few years ago)
John Jones tells me that Philadelphia's WJJZ (106.1 FM) is an all-jazz station, and from what I've gathered by searching the World Wide Web, there are still a number of all-jazz radio stations, mainly university or "public broadcasting" radio stations
* If anyone ever decides to make a live-action version, some characters appear to be based slightly on real people: Ernie (Danny DeVito), Oskar (Yakov Smirnov, although I've been told the accent is supposed to be Klasky-Csupo co-owner Gabor Csupo's), and Miriam (Shelley Long)...or am I just imagining things? (I have been told that the DJ in "Sally's Comet" is supposed to look like Craig Bartlett, who does the character's voice...and after watching the movie High School High, I wouldn't be surprised if Baoan Coleman is the physical model for Mr. Hyunh as well as the voice)
* In one of the "Nicksclusives", in one scene where Craig Bartlett is talking, there's a small Lisa Simpson doll behind him; "coincidentally", the character Lisa on The Simpsons is actually named after the creator's sister, Lisa...who also happens to be Craig's wife
* When the people in the buildings yell "Arnold", Sid and Eugene have switched places
* ...and just before that point, four boys are pretty much lined up one behind another, as are four girls; how come Sid, Eugene, Ruth, and Sheena aren't there?
* What's Ruth doing with the fourth graders?
* The bus Helga is on has a "Kidbar" ad on its side, and on the back it says "Work or Play, A Ride on the Bus Will Make Your Day" (it's hard to read, but it's clearer in "Downtown As Fruits")
* Somebody Call The Animators: if you watch the opening credits one frame at a time, when the title zooms in to its closest point, you can see a dotted line outline of the title where it was in the previous frame
* Somebody Call Them Again: right after Helga is standing behind the "ARNOLD" on the pavement, when she says "Hey Arnold", her lips move as if she's saying it slowly
Apparently, somebody did call: they fixed this one when they changed the theme music in the fourth season
* When the four boys form their line (just before the adults call out "Arnold"), watch Harold's tooth; it goes from the right side of his mouth (as you look at him) to his left side
* The first time you see the line of girls, Rhonda's shoes are "low-cut", but just before Helga says "Move it, football head", the shoes suddenly extend much higher (like they normally do in the stories)
* In the closed-captioning, when Arnold and Gerald "touch thumbs" (and you hear that "sproing" sound), the caption says "[glass shatters]"