Just the tip.

You slide up into her panties and wiggle inside her rectum, drawing a **** sound as she tries to squeal around your tentacle. Once inside, you widen the tentacle and Carissa's eyes bulge and they shut tight as she tries to push you out. Wow, she's strong. You actually have to harden yourself a little to overcome the pressure.

After settling at a diameter of ~2 inches (Carissa is quaking, eyes screwed shut, no longer concerned about her mother's predicament), you start gently pushing in...and then retracting. Each thrust you put a bit more **** into it, till you start hitting her prostate and she sloooowly starts to relax...just a bit. You feel a bulge start to form in the front of her panties and her expression becomes less strained, a light sweat breaking out on her flushed skin.

It's definitely a different experience, playing with the other human gender. Normally you favor one or the other depending on the species (one usually "tastes" better) but Carissa...feels feminine, other than the obvious discrepancy. If she relates to the female gender more than her sexual organs would imply, maybe you could help her along...

Anyway, this is just idle thought, which should really have no place in the same room as two writhing women.