Sex animations in a "nutshell":

In the last succubus and demon animation, VR AnimeTed said something about how he analyzed the animation and i want to explain it a bit better. I reccomend you to read his comment so you'll understand what i'm gonna say

"It's hypnotic, but more for the technical analysis.  As I learn more about animation and practice more I study everything I see.  So here I'm watching the wave from the primary motion of the thrust, to the hips to the thighs to the feet.  Great example of how to really elevate an animation with minimal movement through subtle attention to detail.  And that's without thinking?  pffft, maybe one day I'll be able to knock something like this out without thinking, lo"

So my tip is... and this took some time to figure out on my own. That you can imagine a human body as a chain. In a conceptual way. The chain is not a solid object, neither it is the human body. So if you grab a chain from the ground the first links moove with your hand and the rest moove as a consecuence of their "parents" (previous links) and they don't follow the exact path. Same happens with the human body. Let me explain, but for that I need you to open the succubus and demon animation in a new window, and look at it as you read the following:

Here it is:
https://gfycat.com/activebackcapybara

So now, if you notice, the main action is being done by the demon guy's penetration. And the succubus body mooves as a consecuence of tit. well, the first thing that reacts is obviously her hips that moove back almost, at the same time as the dick "hits the end" (look at it now) I say almost, because it has to have some delay. All impacts have some kind of delay due to impact absortion as if you watch some slow motion punch in the face, the face doesn't moove immediately, it takes some time to move because at first it tries to absorb the impact. so always give some small delay to reactions based on impacts.

The next thing that mooves is the chest since it's directly connected to the hips with the spine. they should almost moove at the same time but add some really small delay to that too for the same chain principle. (Look at the anim again)


Then it should be the head. You're starting to get it right? neck and head moove as a consecuence of that chest moovement, but since they're more far away they should have some delay compared to the chest. So: Hips moove first, which as a consecuence results in some chest moovement that generates a reaction in the neck and finally the head.
The head is the end of the chain so it should moove more freely. (If you were holding that chain you grabbed from the ground before and give it a wiggle, the part close  to your hand mooves immediately, but almost mooves as much as your hand, while the last part goes crazy but starts mooving latter)

As a consecuence of this main spinal moovement it generates a reacion in the limbs of our character. that should follow the same hierarchy as before. ALWAYS keeping in mind where the forces come from and bone hierarchy. since the main action is in the hips, knees should moove right a bit latter than the hips and as a consecuente of the hips, the feet would moove after them. check again the animation and pay attention to how the hips moove first, then the knees and then the feet.

The same happens with the arms in this case, but since they're not really visible i didn't care much about them ( i did mooved the shoulders a bit since it somehow looked natural to me)

As a conclusion. always keep in mind where your main action is and imagine the consecuences of that moovement. so for example in an animation where the guy is fucking the girl's mouth, the main moovement is in the head that would trigger a latter moovement in the neck, the the chest etc.

Hope this block of text helped you guys somehow <3