Alec turned back to him to tear him down again. Alec was not a dog and he would not sleep at the feet of anyone, when he heard the sound of a zipper and his eyes went south and oh....his brain completely shut down. He was vaguely aware that Magnus was still taking about something, but Alec's eyes and his brain was still on the zipper.
Alec had not seen anyone other than his family, because of various reason, one being that they shared a tent in the camp, but this was something totally different. His mind was trying to picture it and that was really not helping. He was also starting to get hard, again, but this time he either didn't care that Magnus might see, or he just didn't know.