For the curious or uninitiated, sliding refers to stacking women on top of one another as the guy alternates his individual pelvic plunging into whichever of the four holes suits his fancy.
Normally the women face the same direction (or each other). In one scene they spice it up as Natali and Natasha bravely assume the awkward position of stacking themselves back-to-back as they are plundered by one of the uncredited male performers who make up a third of each threesome.
Overall, the women are exceptionally pretty, young, and receptive to intrusions - be it dicks or toys. The brief girl/girl before the man joins in is a perfect warm-up to the sliding and other less acrobatic sex.
Pre-nom for Best Foreign All-Sex Release.