Very hard and yes. You're not washing that stuff off. That's one reason for having a cutoff. If you went to a shady nightclub with cocaine use, you might get it on you despite never knowingly touching it.
Even if you just have a job handling cash, in some places as much as 90% of currency has cocaine on it in some amount. That's why they have these cutoffs. It's entirely possible to have some minimal contact with and absorption of cocaine without doing anything even slightly dodgy.
Not it wouldn't have been. He's been declining at an alarming rate for like six months and was visibly on coke on stream. It was only a matter of time. Predicting 26 grams would have just been seen as a bit of an exaggeration.
He was taking "bathroom breaks" on a regular basis and showing back up obviously coked out of his mind, even though it wasn't until the final cokestream (where he literally showed up with coke on his nose) that it was entirely undeniable.
How did they obtain the sample? I find it more plausible that the sample was contaminated, e.g. asking the kid for her comb or brushing her hair and getting one of Kayla's, versus Nick treating his kids with medicinal cocaine. I just think he would consider it wasteful.
They generally take it directly from the child's head, and it is immediately put in a bag with an identifying number/barcode/whatever on it that is then filed with the subject's name. Any possibility of it being accidentally switched is nearly eliminated.
If Nick thinks he can "prove" this, unless it really did happen, he's living in a fool's paradise.
I'm also disinclined to think that if a child is living in a home with a bunch of cokehead sex perverts who are completely out of their minds on coke and coom, where dealer level quantities of cocaine were found, and somehow tests positive for coke, that this is somehow an accident.
This is some Occam's Razor shit. The simplest explanation is that the kid was, indeed, exposed to enough coke, for whatever reason, to test ten times the threshold level. The alternative requires extensive incompetence beyond anything reasonable, or a conspiracy.