Harmony
The Clarinet in A and Bass Clarinet are harmonized in fourths and are descending chromatically while the bassoon continues it solo. The bassoons second to last note on measure 5 is a Gb which is played by the piccolo clarinet at that exact moment to sound like it's played on the same instrument.
Technique
In order for Stravinsky to have long wind passages without the wind players running out of breath he would let wind players share a line of music; for example, at the start of measure 4 the Clarinet in A sounds like it has a continuous line until measure 9, but on measure 6 the first clarinet player stopped playing and the second clarinet player continued the line. A similar instance occurs in this section with the bassoon and the piccolo clarinet, but it's not for the same reason, it is for a timbre effect.
Texture
In order to achieve a dark and mysterious sound, Stravinsky used the chalumeau register of the clarinets.