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Experiments suggest that infants may expect someone who shares food with another person to respond when that person is distressed. But a 2025 replication supported only one of the original study’s two gaze measures, and neither experiment established that saliva itself—not feeding or food-sharing—was the cue.
What the experiments suggest about infants and close relationships
A 2022 study in Science reported that children, toddlers, and infants use saliva-sharing interactions as a cue to infer a distinctive relationship. The authors describe close relationships as involving strong attachments, obligations, and mutual responsiveness. In the infant experiment, the researchers interpreted looking behavior as evidence that infants expected a person who had shared saliva with a puppet to respond when the puppet became distressed.
This is an interpretation of infants’ expectations in a constructed scenario—not evidence that babies consciously understand adult ideas such as intimacy or love, or that saliva exposure creates a bond. The study’s abstract summarizes the broader finding: “We found that children, toddlers, and infants infer that dyads who share saliva (as opposed to other positive social interactions) have a distinct relationship.” The paper was published in Science in 2022.
How the infant test worked
The original infant experiment included 8.5- to 10-month-olds. A puppet shared an orange slice with one actress and played ball with another. Later, when the puppet showed distress, researchers recorded whether infants first looked toward either actress and how long they looked at each. A separate neutral-looking phase checked whether infants simply preferred one actress in general.
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The original study reported that 16 of 20 infants (80%) first looked toward the saliva-sharing actress. That small-sample result was one measure of infants’ response; looking first and looking longer are distinct outcomes.
What the 2025 replication found
Ciftci, Kominsky, and Csibra tested 50 infants aged 8.5 to 10 months in a laboratory, using eye tracking in a close replication of the original infant experiment. Their results were mixed across the two gaze measures:
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| Measure | Original study | 2025 replication |
|---|---|---|
| First look during distress | 16 of 20 infants (80%) first looked toward the saliva-sharer, as reported by the replication paper. | 29 of 50 infants (58%) first looked toward the saliva-sharer; the authors report this did not differ from chance. |
| Time spent looking during distress | The original study reported a preference for the saliva-sharer. | Mean proportion of looking time at the saliva-sharer was 0.59; infants looked longer at that actress, which the authors regarded as a replication of this result. |
| Neutral control phase | A separate phase assessed general preference between the actresses. | The researchers found no general preference for the saliva-sharing actress. |
The 2025 result is therefore a partial replication: looking time aligned with the original finding, but the first-look result did not. The studies also differed in setting and gaze measurement: the original experiment was conducted online with manual gaze coding, while the replication took place in a laboratory with eye tracking. The replication article reports its methods and results.
Why saliva may not be the signal
In the videos, saliva itself was not visually accessible to infants. Sharing a bitten or licked piece of food also involves feeding and food-sharing, which could signal care or closeness independently of saliva. The replication authors say their experiment could not determine which part of the interaction drove infants’ responses.
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To isolate the cue, future experiments would need to distinguish feeding without saliva-sharing from saliva-sharing without feeding. Until that is tested, the findings support a possible inference from a food-sharing interaction, not a conclusion that saliva alone signals a close relationship.
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What to take from the evidence
- The original experiment suggests infants may expect a person who shared food with a distressed puppet to respond to it.
- The external replication found longer looking toward the saliva-sharing actress, but did not reproduce the original first-look result.
- The small experimental samples and gaze-based measures do not establish a universal rule about how infants interpret relationships in everyday life.
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