"Mention", not "tuck ankles behind one's ears when another guy walks by" or inventing competition. For example "Do you think *random movie* is worth going to see? ( in my case, it was Seven) ______ asked me if I wanted to go, but I didn't say one way or another." My response to the affirmation on the movie was, "Yeah, the movie sounds good. Not sure about the company...." He immediately invited me and we were together for about 18 months.
Then again, I had it on reliable authority that he liked to make the first move, so all I did was give him the opportunity to do so. Your mileage may vary. Ultimately we drifted apart because of a little "what's mine is mine, what's yours is ours" attitude on his part, but we had some fun times. B)
If another guy is mentioned, take the opportunity to ask if that would prevent her from going out for pizza, coffee, a movie, etc. Something casual and one-on-one. You'll never know unless you ask.