Origami sheet

Step 1.

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

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

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

Crease well, and leave it folded.

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

Crease well and leave it folded.

Turn the model over from right to left. Then repeat the manipulations described in steps 2 and 3.

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

Slide the left index finger inside the lower left tip, at the point where the vertical axis of symmetry becomes a slit.

To do this, open the tip and flatten it almost completely.
The left thumb is against a mountain fold, and the left index finger against the corresponding valley fold.

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

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.

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

Slide the right index finger inside the lower right tip.

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

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 regarding the final position of the inverted tip. If it is supposed to be the head, it should then be almost at 45°.

Mark along the tip that has just been inverted, a point that will allow you to invert the tip again inside, downward, so that the end drops slightly.

There is no real reference, it is a matter of proportion to form the head.
to make this inside reverse fold you can proceed in steps:
a. At the marked point, make a valley fold by bringing the tip from top to bottom.
Crease well, then unfold.
b. Transform the previous valley fold into a mountain fold.
Crease well, 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.