SkaaBorn

If you are unfamiliar with Tofu, please read this post or watch this playlist about the snake who hates Markiplier. tl;dr- under the Markiplier gif.

From the videos you can see she tries to figure out what is upsetting Tofu, and found that it's not just streamers, or just his voice, or the stream. This specific snake

He does not like Markiplier specifically which is demonstrated by him squaring up with Mark, striking, and tail buzzing at him. He recognizes Mark specifically as a scary threat.

Animals have been shown to recognize human faces, and Tofu's reaction to Markiplier's face (and only his face as shown by the printout) is strong evidence that he recognizes Mark's face and differentiates him from other faces. With crows, they've been shown to hold grudges and have that grudge extend to other crows.

So Tofu has a negative association with Mark, and specifically Mark. The question is why? My theory is: perceived threat after a perceived dangerous situation. Some have theorized Tofu was mistreated by someone who looked like Mark- if they were while in his keeper's care she'd know. If it was his breeder, he'd more likely be afraid of all humans and need to first get over this negative perception (basing this on how Sakura reacted with massive trauma that took years for her to overcome, and to this day she's still jumpy. A breeder doesn't socialize their snakes so they'd only know humans to be abusive before being adopted, and his current keeper would very much notice that terrified trauma behavior to herself.)

One thing important to know about snakes is they are not only capable of learning from each other, but are protective of each other. I've seen this with my girls interacting with each other (yes snakes have friends and remember their family), learning from watching the other and copying her actions, as well as behavior I've observed on the Rattlecam with wild snakes. Adult snakes teach younger snakes, as well as are protective of them- even if they aren't their own babies. A female was shown on the rattlecam watching over a group of slitherlings that were obviously not her offspring as she was heavily pregnant. IIRC that same female ushered babies to safety after a hawk attack before worrying about her own safety. I've seen it in person as well with my girls, who have shielded each other from perceived danger, and scoria also squared up to something scary in the hall as though she were protecting me. And when it left she immediately went back to being relaxed and cuddly and happy. Snakes have friends that are snakes. It's an outdated belief snakes cannot bond with their keepers, as many do and seek them out for attention. These observations of snake behavior are part of what play into my theory basis.

So what could Mark himself have done? If you watch streamers you'll know Markiplier is known for playing jumpscare games with his FNAF let's plays being some of his most well known. Tofu's owner knows Markiplier, and is actively watching Markiplier with Tofu. More than likely she regularly watches Mark, has watched jumpscare videos, and had Tofu around while doing this.

It's a reasonable assumption. And if Tofu's keeper reacts to Mark's jump scare videos by flinching, looking frightened, or making frightened sounds, it's quite likely Tofu's sees Markiplier is involved every time... and blames Mark. Seeing his keeper get startled, Tofu doesn't understand it's a fun video or that humans enjoy being jumpscared (honestly I don't think I could explain it to him either) so he's learning from his human that Markiplier is a scary threat.

And from Tofu's point of view? He's right! Markiplier is a regular threat that not only (probably) scared his human, but regularly appears to stare him down and even went after him in his own home! And when his keeper scolds him? It's likely the same misunderstanding that dogs have when their owners yell at them to be quiet- they think the human has joined in! Clearly his keeper is joining him in being upset at Mark!