Doctors are trying to determine which limb is controlled by what brain before attempting to separate a pair of conjoined twins who share every vital organ but their brains. The boys, who are not named, were delivered in Mumbai at Sion Hospital in India last Wednesday.

The boys, who weigh a combined 10 lbs., share a heart, kidneys, liver, abdomen and pelvis, Central European News (CEN) reported.

“In medical literature, we have only seen two such cases where one baby has survived when twins had a fused common heart,” Dr. Paras Kothari, head of pediatric surgery, told CEN.

The boys were delivered via caesarian section, and their mother is said to be stable but extremely distraught. Before an operation is planned doctors must determine which brain affects which limb, the report said.

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“When they are asleep, we will pinch each limb to check which baby reacts. Based on our understanding of whether one baby has all sets of limbs intact, we will proceed to separate him from the second,” Kothari told CEN.

Conjoined twins occur once in every 200,000 live births.