Final answer:
Amy Tan uses the comparison of squid to bicycle tires to illustrate the squid's grooved surface, due to the crisscrossed knife markings.
Step-by-step explanation:
In the sentence from Amy Tan's "Fish Cheeks," the squid is compared to bicycle tires to illustrate the grooved surface created by the crisscrossed knife markings. This comparison highlights the visual pattern and texture of the squid, which is reminiscent of the treads found on the tires of a bicycle. Therefore, the correct interpretation of the comparison is that the squid have a grooved surface, not necessarily that they are round in shape, black in color, or unappetizing.