I picked this up from Language Log, where they’re discussing the fact that Britney Spears uses a linguo-labial /l/ in several music videos. The video which proves this astounded me:

For those of you who aren’t linguists, let me explain what makes this so remarkable. As the above video shows, when Britney is pronouncing an “l” sound, she doesn’t merely place her tongue against the back of her teeth, as is normal for English speakers. Instead, she sticks her tongue out of her mouth and presses it against her upper lip. This sort of articulation is known as linguo-labial (or apico-labial) because it involves both the tongue and the lip. Now, linguo-labial sounds are extremely rare in the world’s languages, and are completely unheard of in English. So video above appears to present an unprecedented native English speaker who at least sometimes pronounces /l/ with a linguo-labial articulation.

Except maybe not. The commenters at the Language Log come up with a better hypothesis: this is a lip-syncing technique for exaggerating the articulation of the /l/, to aid in matching up video with audio and provide stronger cues for viewers. Commenters dug up music videos of other performers with the same articulation, though this is slightly mitigated by a live video of Britney which shows her doing the same thing. Unless you think that (heaven forfend!) Britney may have lip-synced a live performance.