Poser uses spline animation by default. That means that every movement will continue in a curved line from every keyframe you set - if your fingers were moving to close, they'll close a little further before trying to get back to what you set next, because it's trying to make that curve.

In the Animation Palette you can set this behaviour differently. Go there, select the body parts you wish to configure, then select the frames for them you want to affect.

Those three icons up there, right after the add and delete keyframe buttons, change the movement behavior. First one is the default spline section - that makes every rotation and position change into a curve. The second one is the linear section - it'll make the frames between your two keyframes in a straight line. Third one is the constant section, it'll keep the rotations and positions the same until you change them in a keyframe - this is the one you want for this.

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Feel free to call me Ohki!

Poser Pro 11, Poser 12 and Poser 13, Windows 10, Superfly junkie. My units are milimeters.

Persephone (the computer): AMD Ryzen 9 5900x, RTX 3070 GPU, 96gb ram.