Demai 3:2-3

Demai 3:2

If a person wants to lighten his load of vegetables by cutting off the leaves, he must tithe them before he throws them away. (This is because an unlearned person might find the leaves and eat them without taking tithes.) If someone takes a bundle of vegetables in the marketplace and wants to return them, he must take tithes because he acquired them. If he is still selecting and wants to trade the bunch in his hand for a better bunch, he need not tithe the ones he’s returning because he has not yet acquired them.

Demai 3:3

If someone finds fruit on the road and takes it intending to eat it, but he then decides to save it, he may not put it away until he has tithed it (because he acquired it). If he took it to keep it from getting lost, he need not tithe it. Whatever one may sell in a doubtful state of tithes (as discussed earlier) may not be given as a gift in a doubtful state of tithes. Rabbi Yosi permits untithed produce to be given as a gift so long as the giver informs the recipients that tithes must be taken.