In 2012, researchers at Cornell University prepared a test for 200 children aged 8 to 11. They were presented with the option of having a cookie or an apple as a snack during a school lunch period. Most children chose the cookie.

Then, researchers conducted a second trial. They offered the same cookie or apple, but this time the apple came affixed with a sticker featuring Elmo from Sesame Street.

Kids in the first group chose apples at a rate of 20 percent. Kids seeing an apple with the sticker picked the apple at a rate of 40 percent. The mere presence of Elmo encouraged children to choose the healthier food option at double the rate of the unstickered fruit.

It’s clear that Elmo—the red-furred, hyper, inquisitive Muppet—strikes a chord with kids. Youngsters tend to stop what they’re doing when he appears on the screen, gripped in a kind of hypnosis. Tickle Me Elmo was one of the toy industry’s biggest success stories, causing long lines when it debuted in 1996. Its appeal wasn’t lost on adults, either, with the vibrating toy soothing the famously stoic Bryant Gumbel during a Today show segment on holiday gifts.

But for children under the age of 4, there’s quite a bit more working in Elmo’s favor than simply being cute. In many ways, he was engineered to resonate with this target audience, and child behavioral experts think they know why.

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Visually, Elmo presents as a very atypical presence on camera. He’s virtually the only red Muppet in the show’s cast of characters, which is relevant because young children tend to see bright colors like red more vibrantly at a young age than muted colors. (Brown, for example, tends to bore babies.)

Once Elmo has captured a kid's attention, he manages to keep it by speaking in a unique cadence that some child psychologists have dubbed “parentese,” a gentle vocal rhythm that kids associate with the authority, warmth, and calming effect of their guardians. By speaking in the third person (“Elmo likes you!”), the character also becomes relatable: Young children tend to conceptualize themselves in that manner as they learn their way around language.

"His speech style is 'mother-ese,'" Dr. Lauren Gardner, administrative director of the Autism Center at Johns Hopkins All Children’s Hospital, told CafeMom in 2018. “The high-pitched voice, dragged-out vowel sounds, and exaggerated inflection is how most children are spoken to by caregivers in our culture.”

Initially, Elmo didn’t have much to say. When the character made his first appearance on Sesame Street in 1985, he was not the giggling, slightly mischievous Muppet that was fleshed out later. At first, producers at Sesame Workshop knew simply that he would share many of the same traits as the toddlers watching him on television. He would be open-minded, curious about the world around him, and generally upbeat. By mimicking many of their attributes, he would capture their attention.

"[Elmo is] just like toddlers who are in an exploratory stage of life,” Dr. Tovah Klein, director of the Center for Toddler Development at Barnard College, told Slate in 2013. Both kids and Elmo are “like little scientists, trying out and exploring what is around them, delighting in it.”

For some kids, Elmo speaks to them. For others, he speaks for them. Either way, he’s far more likely to keep a child’s attention than most children’s show characters, relatable in virtually all ways. Except for the fur.