The horizon in the west is where Sun disappears in late afternoon. In the morning when Sun reappears in the east he is like a newborn baby, at noon he is standing tall, and in the afternoon he shrinks - he is growing old. His disappearance in the west was called 'the biting of the sun' (Chikin) by the Maya:

"The manik, with the tzab, or serpent's rattles as prefix, runs across Madrid tz. 22 , the figures in the pictures all holding the rattle; it runs across the hunting scenes of Madrid tz. 61, 62, and finally appears in all four clauses of tz. 175, the so-called 'baptism' tzolkin. It seems impossible, with all this, to avoid assigning the value of grasping or receiving. But in the final confirmation, we have the direct evidence of the signs for East and West. For the East we have the glyph Ahau-Kin, the Lord Sun, the Lord of Day; for the West we have Manik-Kin, exactly corresponding to the term Chikin, the biting or eating of the Sun, seizing it in the mouth." (Gates, a.a.)

The first 4 pictures show east, north, west, and south. The lower two glyphs represent 'Lord' (Ahau) and 'grasp' (Manik). Manik was the 7th day sign of 20 such and Ahau was the last of them.

I imagine the 'Lord' was Sun and that in Likin (east) we see him (at the top formed like an inverted Ahau sign) depicted in triplicate, viz. as Morning, Noon, and Evening Sun. The 20th day sign, Ahau, will therefore be the upside down situation, with Noon Sun at the very bottom.

When Sun goes down at the horizon in the west it is a sign of the arrival of darkness. In order to 'come alive again' in the morning the day after, the fire of Sun must be rekindled. I imagine the following Maya pictures tell about the process, in which at bottom the 'grasping hand' returns the 'fire':

(Gates: Dresden tzolkin 15)

When 'rattles of serpents' (tzaab) are mentioned together with 'the biting of Sun' (Chikin), it probably is because these rattles are the dried out old remnants of the serpents. To kindle a fire you must have completely dry stuff to work with.