A Gentile woman says even dogs deserve crumbs; Jesus heals a deaf man, heals many others, feeds 4000 people, refuses the Pharisees and Sadducees a sign of His authority (again), then has to explain to the disciples what He means by the yeast of the Pharisees and Sadducees: Mark 7:24–30; Matthew 15:21–28; Mark 7:31–37; Matthew 15:29–31; Mark 8:1–10; Matthew 15:32–16:4; Mark 8:11–21; Matthew 16:5–12
The arguments that are too tricky by half: show us a sign, don’t heal on the Sabbath, wash your hands … all within the letter of the Law, or the Pharisees’ interpretation of the Law, none within the intent of the Law.
Warning against taking the Pharisees’ and Sadducees’ approach to God too seriously, Jesus told His disciples:
Matthew 16:6 Watch out! Beware of the yeast of the Pharisees and Sadducees.
It takes only a spoonful of yeast to make a whole loaf of bread rise well—so you don’t need a lot of deceptive (or false, or tricky) teaching to affect everything you believe.
Update: see also Jesus and Purity (Part 1: Hand Washing)