Origami sheet

Step 1.

Make a bird base, placing it so that the two long points separated by a slit are oriented at 6 o'clock.

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The upper half has 3 superimposed triangles:
at the front, a large one of double thickness, with a slit on top at the vertical axis.
in the middle, a small one of quadruple thickness, with a closed upper point.
at the back, a large one of double thickness, with a slit underneath at the vertical axis.

Step 2.

Form a valley fold by bringing the lower right edge of the front right flap from right to left along the vertical symmetry axis.

Crease well, and let it fold.

Step 3.

Form a valley fold by bringing from left to right, the lower left edge of the front left flap, along the vertical symmetry axis.

Mark the fold well, and let it fold.

Step 4.

Turn the folding from right to left. Then reproduce the manipulations described in steps 2 and 3.

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You now have at the bottom of the folding two very sharp, thick points.

Step 5.

Place the left thumb between the two lower points, along the vertical slot.

Slide the left index finger inside the lower left point, at the place where the vertical symmetry axis becomes a slot.

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To do this, open the point and lay it almost flat.
The left thumb is against a mountain fold, and the left index finger against the corresponding valley fold.

Step 6.

With the thumb, lift the tip in order to fold it inside itself as high as possible.

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The mountain fold against the thumb becomes a valley fold.
The valley fold against the index finger becomes a mountain fold.
There is no exact reference for the final position of the folded tip. If it is to be the tail, it should then be almost horizontal, slightly angled upwards.

Step 7.

Place the right thumb along the mountain fold of the lower right tip.

Slide the right index finger inside the lower right tip.

additional information

To do this, open the tip and lay it almost flat.

Step 8.

With the thumb, lift the tip in order to fold it inside itself as high as possible.

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the mountain fold against the thumb becomes a valley fold.
the valley fold against the index finger becomes a mountain fold.
There is no real reference for the final position of the reversed tip. If it is supposed to be the head, it should then be almost at 45°.

Step 9.

Along the tip that has just been reversed, mark a point that will allow you to reverse the tip again inward, downward, so that the end drops slightly.

additional information

There is no real reference, it is a matter of proportion to form the head.
To make this inner reverse fold, you can proceed in steps:
a. At the marked point, make a valley fold, bringing the tip from top to bottom.
Crease the fold well, then unfold.
b. Transform the previous valley fold into a mountain fold.
Make a strong crease, then unfold.
c. Place your thumb inside the tip (between its two flaps) at the marked point.
d. Tilt the end of the tip toward the side where your thumb is placed. The initial mountain fold between the marked point and the tip's end has turned into a valley fold.
e. Remove your thumb from its position, then close the flaps of the tip that had been spread apart to place the thumb.