If you're curious how to crochet on flip flops, this post will answer all your questions including if they fall apart over time. Great free tutorial on how to get started crocheting shoes and boots for spring, summer, fall, and winter.
use this technique in order to emphasize the contour of the object. To do it you have to entwine two warp threads (front and back) with the working thread. To make a contour we usually use thicker threads.