Aliasing arms_behind_head → hands_behind_head
Link to alias

Reason:

Even though having just your hands behind your head technically isn't the same as having your hands and arms behind your head, I've noticed these tags are usually reserved for the exact same kind of pose:

post #542657

So that definitely could use an alias. Doesn't really matter which way, though I personally do think hands sounds more natural. To be honest, sometimes (if rarely) one comes across something like this...

post #603786

...where the entire arms are behind the character's head, resulting in a slightly different pose, but it's not as if anybody makes the distinction when tagging. Whether it ends up getting one tag or the other seems entirely random.

Oh, and then there's the very much comparable case of hands_behind_back and arms_behind_back:

post #625232 post #582250 post #565279

Same goes for them, I see little reason not to alias here.
And I haven't even mentioned the singular versions of all of these (hand_behind_head etc.), so to summarize:

• arms_behind_head -> hands_behind_head
• arm_behind_head -> hand_behind_head

• arms_behind_back -> hands_behind_back
• arm_behind_back -> hand_behind_back

I'd have no problem with most of these, but hand/hands_behind_head almost seems worth keeping both, almost. For example:

post #662865

Very specific pose, and probably common enough to tag by itself. I don't really have a solution for this, but I thought it would be worth bringing up at the very least.

hand_behind_* is only used for when a single arm is used, whereas hands_behind_* is supposed to be for when both arms are used. However, the arm(s) -> hand(s) aliases are good, so I've made the following changes:

• Alias: arms_behind_head -> hands_behind_head (OP approved)
• Alias: arms_behind_back -> hands_behind_back (approved)
• Alias: arm_behind_head -> hand_behind_head (approved)
• Alias: arm_behind_back -> arms_behind_back (deleted)
• Alias: arms_behind -> arms_behind_head (deleted) - Just as likely to end up in either, so this was a bad alias
• Alias: arm_behind_back -> hand_behind_back (approved)