When feeding their babies, parents will chop, dice and mash foods to make them easier to eat. But most stop short of chewing the food and spitting it into their babies' mouths.

Not Alicia Silverstone. The actress posted a video on her blog " The Kind Life" on Friday of herself baby bird-feeding her 11-month-old son Bear Blu.

"I fed Bear the mochi and a tiny bit of veggies from the soup…from my mouth to his. It's his favorite…and mine," she wrote. "He literally crawls across the room to attack my mouth if I'm eating. This video was taken about a month or 2 ago when he was a bit wobbly. Now he is grabbing my mouth to get the food!"

Although Silverstone's mouth-to-mouth may be prompting a collective "eww" around the Internet, the practice, technically called premastication, is not uncommon for mothers and babies around the world. Dr. William Schaffner, chairman of preventive medicine at Vanderbilt University, said it's not necessarily as unsanitary as it might seem.

"For conventional germs this is not a big issue. When we kiss our babies, the bugs that we all have resident in our mouths are likely to be transmitted to the baby," Schaffner said.

However, Schaffner said the practice becomes unsafe if the mother has an infection, such as hepatitis B, which could be transmitted to her baby. In fact, the U.S. Centers for Disease Control and Prevention specifically warns mothers with hepatitis B not to pre-chew food for their babies.

Keith Ayoob, an associate professor of pediatrics at Albert Einstein College of Medicine in New York, said pre-chewing food is not something he would recommend for children who should be learning normal eating habits from their parents.

"That falls into the category of above-and-beyond parenting. The child needs to learn how to chew," Ayoob said. "The list of reasons for not doing this is miles long."