Glitch Kisses
Okay, glitch kisses.
Neither Error nor Blue really have had much... romantic interaction--glitch's pain and haphephobia and all--so when they do finally get comfortable enough with another person, they kind of only know what they've seen on TV which won't work because they don't have lips, only bone.
What they do know is that usually, tongues are involved somehow.
Hence why the first time Nightmare agrees to let one of them kiss him, he is sincerely confused when a set of five tentacle tongues flick over his face.
They do the snake's tongue flick with their tongues over his teeth and he very sincerely perplexed.
Nightmare: Surely... Surely this is a glitch thing. Error: Are we doing this right? Blue: Well he isn't mad! I say we go for it.
Blue: You... You taste really good, Nightmare. Nightmare: ... Thank you? Error: He tastes sweet and floral. Blue: Mhm. I like it. Nightmare: ... I'm just gonna take it as a compliment.
Of course, Nightmare has his own weird habits such as his blooming season (a story for another time), so he just assumes this is a glitch custom that he didn't know about and goes along with it.
No one says anything until Geno does.
Blue: Morning, Nighty. *licks face* Nightmare: Morning, Blue. Error: I want some. *licks face* Geno: across the table ... What the hell are you two doing? Nightmare: Wait, is this not normal? Geno: ... Noooooo? Why would this be a thing? Nightmare: I don't know, there are cultural differences between me and normal skeletons, why not glitches? Geno: What cultural differences--Do you mean to tell me you think this is normal for glitches?! Nightmare, what culture would they have even gotten that from?! I get you don't know where Error came from, but Blue’s from Underswap! Nightmare: But... But I thought I was doing this right— Geno: No one licks other peoples' faces, you three!
Geno is unfortunately the only other glitch that they talk to on a regular basis and he only has one tongue, so he certainly does not do this. He's the only one in the Glitch-Parasite family that doesn't have the extra tongues.
This gets even worse when Dream finds out.
Dream: Are you... LICKING my brother?! Blue! Blue: I DON'T KNOW HOW TO KISS AND ERROR DID IT FIRST AND NIGHTMARE DIDN'T SAY ANYTHING SO I JUST WENT WITH IT! Dream: Error! Error: I DON'T KNOW HOW SKELETONS KISS! I'VE NEVER KISSED BEFORE! I PANICKED! Nightmare: More importantly HOW DID YOU GET INTO MY HOUSE? Ink: Aww, last time I licked a person they screamed at me! *pouts* Error: It's because you don't have the extra tongues, Squid. *sticks out said tongues* Ink: ... *snaps his fingers* I can probably fix that. Dream: INK DON'T YOU DARE.
Thus Ink became envious of the glitches for their tongues, and Error and Starberror/Blueberry learned that licking people is only okay if you love them.