My Model Son

Never heard of dental floss in shampoo ads, each ad has its own techniques to acheive various things. Definitely, though, shampoo is a top payer, lead roles in a shampoo ad (for adults) are 100,000+ jobs generally. People have done a lot of bad things, for less money.

As the lead model walked two assistants walked on either side holding a piece of dental floss that stretched under her hair. As she moved they would bounce her hair up and down to give the impression of natural movement. The dental floss is either invisible on film or edited out--I don't know.