Batman and Robin
Trick ID: 279
Second flyer hangs with their feet in betweeen the thighs of the first.
First flyer swings out and gets up into a sitting position on the bar. The second flyer jumps onto the bar from the platform and swings underneath. At the frontend, the second flyer lifts their legs up (together) and places their feet in between the thighs of the first flyer, who squeezes their thighs shut. They swing back to the platform and out again. As they approach the front end, the second flyer lets go of their hands and opens backwards to catch. This trick is best performed on a bar-to-bar rig where the timing of the catch is less important.
You can find out more about this trick in following books: