Shaun walks over to you, with a quizzical expression, his nostrils flared. He puts his face in front of yours and sniffs it. Then he sniffs downward, moving to your chest, then your armpits. Liking the smell, he tugs at your shirt. "No Shaun," you say, "stop!", but he doesn't understand, or even remember that as a more evolved species he was your brother. He grabs hold of your shirt and rips it off. Burying his nose in your hairy pit, he inhales and grunts happily. Then his head moves to your groin. You had suspected Shaun swung both ways, but you're certainly not prepared for incest with a caveman. You push him away.
Sean doesn't take this lying down. In fact, he makes you lie down, with one big push. His beats his chest with his hands, and then fingers your zipper to pull it down. He licks his lips and prepares to yank down your boxers as you struggle. Then you realize that the hand on your watch has not been turned all the way back. As Shaun succeeds in freeing your cock and putting it in his mouth, you completely return the watch's hand.
Shaun's eyes instantly clear up...and then go saucer-wide with shock and horror. He pulls his face away from your cock as if it was on fire. Staggering backward, he tries to collect his wits. He looks down and sees his own dick is rock hard. "W-w-why am I naked?" he says. "And why was I--Oh God, what the fuck is going on?!"
You desperately think what explanation you could possibly offer. Or should you just use the watch again and shut him up? There's not much time to decide, judging by Shaun's increasing hysteria.