I can think of totally legal hilarious things you could do all day long.
Introduce yourself to the cart folk and be sure to shake the hand of the sister.
Then say, "Oops! Oh no! You're not menstruating right now or having a discharge beyond your period, are you?" (wait for response)
"Because Leviticus 15:25-30 says when I touch women with discharges I will be unclean until evening. Do you have any hand sanitizer?"