I don't know if I'm reading too much in it, but like the poke which was a symbolic moment, I'm wondering if the snake escaping is as well. The forehead touch was telling us that even after Sasuke has upgraded his strength and fighting ability, he is still weaker than Itachi. Kinda brings Sasuke's character down to earth after people were saying he was too strong after the first half of this battle.
the snake thing, I'm wondering that it may be more metaphoric than literal. Thinking it could be symbolizing Sasuke instead of Orochimaru as well. And that it means that sasuke has escaped this fight alive even though he was the one who lost. But the thing that gets me is if it answers Madara's question of whether Sasuke would shed his serpent scales or not. If it is, then its a sign of whats to come in the year of the Sasuke.