What scene of death does Steinbeck describe in the beginning of chapter six ?

From the text:

A water snake glided smoothly up the pool, twisting its periscope head from side to side; and it swam the length of the pool and came to the legs of a motionless heron that stood in the shallows. A silent head and beak lanced down and plucked it out by the head, and the beak swallowed the little snake while its tail waved frantically.

Steinbeck's careful control of setting in the novel is especially clear in this chapter, which finds us back at the beginning - at the brush near the Salinas River. As he did in the opening chapter, Steinbeck begins with a description of nature. Once again, this nature vignette resonates with the themes of the novel. We see the casual violence of nature - the stork devouring the water snake - and we see Lennie's nonchalant integration into this atmosphere as he stoops and drinks with his lips like a thirsty dog.