Do identical twins show anomalous physiological connectedness?

This is the smallest evidence base in the library for any controversy: two pilot studies (Copenhagen and London) totaling 8 twin pairs and 14 sessions. Both studies found that approximately 1 in 4 screened pairs showed significant physiological synchrony, but overall results were marginally significant at best. The strongest finding came from the Copenhagen study's monochorionic-monoamnionic twin pair (sharing same placenta and amnion cavity), which has led to speculation about embryonic entanglement. The London study had methodological limitations compared to Copenhagen (iPhone SMS timing vs. atomic clocks, no inter-rater reliability check). The key missing elements are: (1) independent replication by a laboratory other than Parker/Jensen, (2) larger sample sizes with pre-registered analysis plans, and (3) exploration of whether the monochorionic-monoamnionic subgroup shows systematically stronger effects. The Duane (1965) EEG study in Science provides historical precedent but used different methodology. This controversy remains in the exploratory pilot-study phase.