G-d rhetorically asks Moshe: If [Miriam’s] father spat in her face, would she not bear her shame for seven days?
The word for “spat” is yarok. It is used with meaning in two other places: If the one with a discharge spits on someone who is pure (L. 15:8) and when a man refuses to do his duty and marry his brother’s childless widow:
his brother’s widow shall go up to him in the presence of the elders, pull the sandal off his foot, spit in his face, and make this declaration: Thus shall be done to the man who will not build up his brother’s house! (D. 25:9)
OK. That seems simple enough. Yarok means to spit.
Except that yarok also means something else – seemingly something quite disconnected from spitting: it means “green” and refers to plant life:
And to all the animals on land, to all the birds of the sky, and to everything that creeps on earth, in which there is the breath of life, [I give] all the green (yarok) plants for food.” And it was so. (G. 1:30) … Every creature that lives shall be yours to eat; as with the green (yarok) grasses, I give you all these. (G. 9:3)
How does the color green relate to spitting?!
Well… perhaps the verses dealing with tzaraas, the spiritual ailment, sheds some light:
if the affection in the cloth or the skin, in the warp or the woof, or in any article of skin, is streaky green (yarok) or red, it is an eruptive affection (L. 13:51) and If, when he examines the plague, the plague in the walls of the house is found to consist of greenish (yarok) or reddish streaks that appear to go deep into the wall (L. 14:37)
So… green is connected to tzaraas. But what causes tzaraas? Acting selfishly and in so doing, harming others (anything from gossip to murder). Green is the way of nature – every plant and animal for itself, without consideration. It is not the way in which the Torah commands us to live.
In a nutshell: In the Torah, the color green is never used for holiness (the color is not found anywhere in the tabernacle or anywhere else relating to holy relationships). Instead, the color green refers to acting in a way consistent with nature: in the moment, instinctively, and without thinking.
Thus:The land of Egypt from which you have come, where you planted your seed and irrigated with your foot, like a green (yarok) garden (D. 11:10)
In the Torah, Egypt represents harmony with nature, and growing crops could be done merely using the part of our bodies closest to the ground. Egypt was green – but the Torah never describes Canaan/Israel with that word.
And so, too, does spitting. A father who spits in the face of his daughter is a man who, whether justified or not, has lost control of himself. There are no winners when people lose control of themselves.
Similarly, a daughter who acts in such a way to enrage her father is also culpable (which is why she is shut off for seven days as a result). What would a girl do that would so enrage her father? The most likely explanation would be that she, in turn, did not act morally, and instead chose to indulge her baser desires. As I said, there are no winners when people act like animals.
The widow who spits on her ex-brother-in-law is expressing her contempt for his selfishness, his unwillingness to do his duty and honor his brother’s memory. So she spits on him.
And thus the pun is explained!