Various halachot relating to how a worker can eat in the field he is working in are derived from the verse about picking in the vineyard. One of those is that he is not obligated in tithes. The gemara then brings in two opinions about when one is obligated in tithes – when the food goes into the courtyard or into the house. The gemara then questions why is the drasha from the Torah necessary if the worker was in the fields – wouldn’t he be exempt anyway on a Torah level if he was a buyer who purchased the produce while it was in the field? Various other questions are also raised against the two opinions and answered up. Then the gemara proves how we can derive that an animal can’t be muzzled to prevent him from eating – both produce that is detached and attached to the ground. And likewise, from where we can derive that a wroker is allowed to eat produce that is attached to the ground as well as produce that is not attached to the ground.