The 2-month-old baby looks exceptional. She’s crawling forward at an age when most infants cannot even roll over. Another tiny infant sits straight up when her foot is tickled.

Sometimes the parents are pleased, and see these behaviors as a sign that Zika may not have damaged their babies as badly as they feared.

Alice Vitoria Gomes Bezerra, who has microcephaly, is held by her mother Nadja Cristina Gomes Bezerra in Recife, Brazil. Mario Tama / Getty Images

But in fact, these reflexes are a sign of the profound mess the virus has made in their developing brains, said Dr. Vanessa Van der Linden, the pediatric neurologist in Recife, Brazil, who sounded the first public alert about Zika.

“That is not usual. That is not normal,” Van der Linden told a meeting on Zika virus in babies sponsored by the (NICHD) National institute of Child Health and Human Development, one of the National Institutes of Health in Bethesda, Maryland.

The reflexes making these young infants seem so developmentally accelerated come from the brain stem, and they are supposed to stop a few weeks after birth. They’re the same reflexes that cause a newborn to grasp her father’s finger or root for her mother’s breast.

The pediatricians, neurologists, and child development specialists in the small meeting room gasp and murmur as Van der Linden shows videos of some of the babies she’s treated at her clinic.

They squall and stiffen their limbs in a way familiar to pediatricians who deliberately startle young infants to check their reflexes.

But these babies aren’t startled, and they don’t relax as they should after a few seconds. They stay stiff — the medical term is hypertonic. And they cry.

“They cry a lot,” Van der Linden told the meeting. “Sometimes they cry 24 hours a day.”