Why do some women play with their clits while being fucked ?

[ban908463]

I see this sometimes on films and wonder why ?

When they're being fucked, isn't that enough stimulation.

I get the feeling - and I could be wrong here, so please correct me - that they're not enjoying the fucking part, so they stimulate their clits to make up for this.

The other theory, is that they do this to keep their pussies wet, so that the sliding in and out of the penis is not painful. Why not use lubricant then ?

Any answers ?