Let your girlfriend tell a joke, so that you must guess when you see her tomorrow. But it doesn't sound like a joke to me, but it sounds like a riddle.

The blind man and the lame man crossed the river together. The blind man walked into the river with his cripple on his back. The blind man said, what's that noise? The lame man said on the blind man's back that someone was taking a bath. The blind man took it and said it was a woman. The lame man said, if you can't see, how do you know it's a woman? The blind man said: Your penis is against my waist.