There was a lot that scared me or creeped me out when I was little.
For example:
The Sherlock Hemlock song "X Marks the Spot" really scared me because of the skull & crossbones for the lyrics "Sometimes it means there's pirates, or at worst it means there's poison..."
Similarly, one of the Roosevelt Franklin Elementary School segments, in which Roosevelt whispered out the letters "P-O-I-S-O-N", and they appeared in the air, followed by a skull & crossbones, scared the **** out of me.
I think this could have been due to a run-in I had with a bottle of highly poisonous Russian perfume when I was a toddler. Being rushed to the hospital and dosed with ipecac which makes you hurl violently, then being dosed with vile black charcoal solution to try to make you stop hurling violently (and which didn't work, because I hurled the stuff up three times on the way home in the car)---well, it would tend to make you extremely nervous around anything to do with poison, wouldn't it? The worst of it was that I hadn't drunk any of the perfume, only spilled it on myself. But Mom and Dad knew how deadly Russian perfume was, so they insisted on rushing me to the hospital immediately. I was also extremely frightened of the animated "Mr. Yuk" PSAs that ran on the Buffalo network stations in the 70s, so I think my theory on this is a good one.
S.A.M. the robot creeped me out because of his strange mechanical noises.
And I, too, was uneasy about the sinister nature of the Lefty segments---especially "The Golden AN".
Seeing the "Willy Wimple" anti-polution segment recently, I still felt somewhat unsettled by it. There was a similar segment that aired on "The Electric Company", for "T-I-O-N", which showed, among other things, fish and birds dropping dead in their severely polluted water and air, and promised that "Pollution means their execution." Very disturbing stuff for little kids to see! What makes it worse is that, since those segments first aired in the 70s, very little has changed. Companies would rather keep right on polluting the world and destroying the ozone layer, because it would eat into their profits if they tried to do anything really worthwhile to fix up the damage. And the politicians won't force them to, because those companies contribute lots of money to the politicians' campaigns. Very sad.
I remember finding Mumford's lack of eyes a bit unsettling. He had big, bushy, black eyebrows, but you never got to see his eyes, did you?
And Mr. Mackintosh, the fruit & vegetable vendor, always looked a bit menacing to me. Maybe it was because he was so quiet. I think I usually just saw him silently pushing his cart through the establishing shot of a street scene, and that was it. I suppose it was because Chet O'Brien was busy with his "real" job of being a techie on the show.
I wasn't frightened by the animated typewriter getting stuck in the umbrella, but I was very frightened when he discovered his ribbon was dry, so he poured in a bottle of ink, which leaked out and flooded the entire screen, turning it black.
There was another animated segment along the same lines, in which a bird dipped its long beak into a big bottle of ink and wrote the word "INK" in the air. Then, it fell into the bottle, clambered out and shook the ink off its feathers, spattering droplets all over the screen. Then, it tipped over the bottle, and the ink poured out, flooding the entire screen and turning it black.
This may have been a clever way for the animators to fade to black, but when you're a little kid with a very literal mind and an overactive imagination, watching it will lead to nightmares! Bad enough to drown in clear water, but imagine drowning in a flood of black liquid you can't even see through!