Most people in the parking lot stopped to stare.

If the sisters were aware that all eyes were on them, they gave no signs. In the supermarket, they ignored the curious glances in the produce section, the startled double takes by the baked goods and the scowls near the cereal. They glided along the aisles, stopping to compare prices on spaghetti sauce.

Two Hispanic children gasped and ran behind their mother. “Why are they dressed that way?” the girl asked her mother in Spanish. “Islam,” the woman said, also telling the child that the women were from Saudi Arabia.

Hebah, who is from Tennessee, smiled at the girl, but all that could be seen of her face were the lines around the eyes that signaled a grin. After nearly a decade under the veil, she and her sister know full well that they are a source of fascination — and many other reactions — to those around them.

Hebah said she has been kicked off planes by nervous flight attendants and shouted down in a Wal-Mart by angry shoppers who called her a terrorist. Her sister was threatened by a stranger in a picnic area who claimed he had killed a woman in Afghanistan “who looked just like” her. When she joined the Curves gym near her home in Edgewood, N.M., some members threatened to quit. “They said Islamists were taking over,” Ms. Ahmed said.

Her choice to become so identifiably Muslim even rattled her parents, immigrants from Egypt.

“I was more surprised than anything,” said her father, Mohamed Ahmed, who lives in Houston with her mother, Mervat Ahmed. He said he raised his daughters with a deep sense of pride about their Muslim background, but nevertheless did not expect them to wear a hijab, a head scarf, let alone a niqab.