It's very difficult, if not impossible, to read the grain for any twist in yew bark. The bark is so flakey, with no real vertical lines as you find with hickory, ash or oak. It's therefore nearly impossible to see if it twists. Sometimes I can see a local twist near a grain abnormality, but this is only seen in the lighter colored underlying bark, and not in the flakes that lay on top of this. I nowadays rely on instinct to make out if a yew trunk will be twisted. Was the tree growing at an angle? Was it exposed to a lot of wind? If the answer to either of these two questions is 'yes', then I assume the wood will be twisted, even if the bark appears straight.
I've used small diameter trees of about 2" diameter and just chopped away with an axe to get only one bow from it. With such a small diameter, you won't be able to get more than one bow from it anyway, so I just don't split it at all. I recently acquired a small trunk that was 2" at the top and 3" at the bottom. It was just thick enough to get two bows from, but then I wouldn't have to rely on splitting. So I used a jigsaw to saw it in half and just ignored any possible twist that would have been present. Although this wood is still drying, I know from past experience that it is perfectly safe to just ignore a bit of twist in yew and saw a log into staves as opposed to splitting.
