One thing Mates does in the book I mentioned is find translators' misunderstandings and prejudices, like the hair-sewing bit in the OP. That also comes up in Lucio Russo's The Forgotten Revolution about the sources on Hellenistic science -- classicists generally aren't scientists either.
(This comment is turning out to sound really hard on classicists, and I certainly don't feel that way. I'm just an interested reader.)
This is a cheap shot, but preparing laserwort or dodo.
More practically, anything that is done by hand and needs a lifetime of training. But you need to be sufficiently specific. No one can use a longbow the way medieval british could, but anyone with a bit of training and a modern compound bow could probably match them. So you'd need to be specific to longbows.
Link: http://borepatch.blogspot.com/2013/06/long-lost-roman-concre...