Rob Roy (1995) - 2 questions

Question: Right at the beginning of the movie, one of Rob's men sniffs at and even takes a bite out of a piece of a cow pat and can estimate the tinkers head start. How is that possible?

Answer: Cow patties leaving the cow and plopping on the ground leave a distinctively odor and start to harden up after a certain length of time. It isn't to hard to speculate that, since these are cattlemen by trade, they would have a systematic way of knowing how long it would take for a cow pie to harden & lose it's odor. Example: they would know that a cow pie left out for 2 days would lose half it's odor & become semi-hard but still have a mushy center.

Question: After Mary is raped, she begins cleaning herself off in the water in front of Alasdair who immediately figures out what happened and of course wants to tell Rob, so he'll avenge her. But she's extremely adamant that Alasdair not tell Rob about it. But if she REALLY didn't want Rob to know, wouldn't she have waited until she was alone to clean herself up? I'm always confused by this, because when she tells Alasdair to keep quiet, she never seems to be hinting that she doesn't really mean what she says. On the contrary, she's very passionate about it.

Answer: She wants to clean herself thoroughly ASAP, so as to avoid pregnancy (though that way doesn't work anyway); if she waited until she was alone, it would've been too late to even try.