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Experiments suggest that infants may expect people who share food in a saliva-sharing scenario to respond to one another in distress. But a 2025 replication found support in one measure of infants’ gaze, not another—and neither experiment established that saliva itself was the cue.
What did the original experiment test?
A 2022 study in Science examined whether infants treat saliva-sharing interactions as a sign of a distinctive relationship. Its infant experiment involved babies aged 8.5 to 10 months. In the key scenario, a puppet shared an orange slice with one actress, while playing ball with another. Researchers then showed the puppet becoming distressed and measured which actress infants looked toward.
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The researchers interpreted a tendency to look toward the saliva-sharing actress as an expectation that she would respond to the puppet. A separate neutral-looking phase checked whether infants simply preferred one actress regardless of the distress scene. The original paper reported that 16 of 20 infants first looked toward the saliva-sharer, a result later summarized by the replication authors. The original authors’ broader abstract states that children, toddlers and infants infer that people who share saliva have a distinctive relationship, compared with people shown other positive social interactions. Thomas et al., Science (2022)
What did the 2025 replication find?
Ciftci, Kominsky and Csibra tested 50 infants aged 8.5 to 10 months in a laboratory, using eye tracking in a close follow-up to the original infant experiment. The results depended on which measure was considered:
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| Measure | Original experiment | 2025 replication |
|---|---|---|
| First look toward the saliva-sharing actress | 16 of 20 infants (80%), as reported in the replication paper. | 29 of 50 infants (58%); the authors reported that this did not differ from chance. |
| Time spent looking during the distress test | The replication paper describes the original finding as a preference for the saliva-sharer. | Mean proportion of looking time at the saliva-sharer was 0.59; the authors regarded this result as replicated. |
| Neutral control phase | Included to assess general preference for one actress. | No general preference for the saliva-sharing actress was found. |
The replication therefore offers partial support: infants spent more time looking at the saliva-sharer during the distress test, but the first-look result did not reproduce the original result. The authors did not find a general preference for that actress in the neutral control. These counts and gaze measures describe two particular experiments; they are not population-wide estimates of what infants believe. Ciftci, Kominsky and Csibra (2025)
Does this show that infants understand close bonds?
No. The experiments measure infants’ looking behavior in staged scenarios, which researchers interpret as an expectation about how characters will act. They do not show that infants consciously understand “bonds,” know who loves whom, or apply a universal rule to relationships outside the experiment.
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The finding is narrower: in these scenarios, infants’ gaze was consistent with treating a shared-food interaction as relevant to whether someone would respond to another’s distress. The mixed results across first look and total looking time are a reason to describe the conclusion as suggestive, not settled.
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Was saliva itself the cue?
The studies do not establish that. Saliva was not visually accessible in the videos, and sharing the orange slice could also signal feeding, care or food-sharing. The replication authors say their experiment could not determine which part of the sequence drove infants’ inferences.
To separate these possibilities, future experiments would need to compare feeding without saliva-sharing with saliva-sharing without feeding. The tested scenario involved sharing a bitten or licked food item; it does not establish how infants respond to every kind of kissing, utensil-sharing or other contact.
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How should the finding be read?
- What the experiments suggest: Infants may expect a person involved in a saliva-sharing food interaction to respond when the other participant is distressed.
- What the replication supports: Longer looking toward the saliva-sharer during the distress test.
- What it did not reproduce: The original pattern in which most infants first looked toward the saliva-sharer.
- What remains unresolved: Whether the relevant signal was saliva-sharing, feeding, food-sharing, care, or a combination.
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