You would think touch spells would be fairly straightforward: You cast a spell, you touch someone or several someones, and effects occur. Unfortunately, the touch spell rules contain the following fatal clause (PFRPG Core Rulebook pg. 213, "Range"):
Some touch spells allow you to touch multiple targets. You can touch
up to 6 willing targets as part of the casting, but all targets of the
spell must be touched in the same round that you finish casting the
spell. If the spell allows you to touch targets
over multiple rounds, touching 6 creatures is a full-round action.
The problem is that a lot of spells include effects that simply don't work under the rules above. Chill touch is the classic example (PFRPG Core Rulebook pg. 255):
A touch from your hand, which glows with blue energy, disrupts
the life force of living creatures. […] You can use this melee touch attack up to one time per level.
A tenth-level caster who happens to have six willing targets (for chill touch, mind) would be allowed to affect them all as part of casting. But if he has seven willing targets, he still would only be able to affect six targets because that's the most he can affect in one round and he's not allowed to use his extra uses of chill touch next round.
Worse, if his targets aren't willing (this is, after all, chill touch), the RAW allow him to affect exactly one target, the one free touch attack he gets as part of casting the spell. The spell allows multiple touches, but makes no provision about spreading those touches out across additional rounds. So the "1 touch attack per level" language is completely wasted.
(Note that the situation would be very different if chill touch had a range of "personal" and gave the caster a touch attack. None of the touch spell rules would apply and so it would actually be a spell consistent with the rules.)
Hide from animals has the same problem as chill touch applied to willing targets: It nominally allows you to target CL creatures. But because of the need to touch all the targets during the round of casting and the limit on the number of creatures touched, it might as well read "Target: one creature touched/level, maximum six creatures".
It seems pretty obvious that none of these results are intended. My question, really, is about the design intent of the "touched in the same round" language. I can't come up with a scenario where it does anything positive for the game. As far as I can tell, we would be strictly better off without it and without any of the scenarios above having to be seriously contemplated in order to understand how a 1st level spell works.
Best Answer
The reason things are worded so badly lies in the 3.0->3.5->PF transition. See below for that! I believe chill touch is still resolvable using the RAW, though.
Chill Touch
The answer to the chill touch question lies in the rules for holding the charge:
Most touch spells discharge after a single successful attack, but chill touch makes it clear that this isn't the case. Instead, you get one touch per level. So the quoted rule allows chill touch to be used across multiple rounds; there's no need for the spell to explicitly state it. (Though it probably should, just for clarity.)
Willing targets
The rules do explicitly state that you can't hold the charge on multiple targets, so no help there! That seems to be the simplest solution, though.
As an aside, an effect that changes the range of touch spells would "unlock" the full number of targets, so there is a technical difference between the current state and your alternate wording. :P
A little bit of history
So why are the RAW in this state? Well, I did a bit of digging, and this thread was very helpful, especially this post by Hypersmurf. (Who I remember from when I posted in the enworld rules forum far too often -- thanks Hypersmurf!)
In 3.0, you could touch 6 willing targets as a full round action, or one as a standard. There was no restriction on touching all the targets the round the spell finished -- in this context the 6 target limit played well with multi-target spells.
In 3.5, the Magic Overview section was changed: the limit of 6 was removed, but the requirement of touching the targets in a single round was added. However, the rules for touch spells in combat left the old restriction of 6 targets in place. The text here directly contradicted that of the overview section. If you assume that the wording of the overview section was what the designers intended, this would still cause no problems with touch spells targeting multiple willing creatures.
In PF, both limitations are included in the overview. I would assume that someone was trying to reconcile the contradiction mentioned in 2, without realizing that it was a holdover from an intended 3.0->3.5 shift. The result? Accidental nerfing of multi-target touch range buffs.
Likewise, the wording of chill touch has been essentially unchanged since 3.0. It's been edited a little to make the wording less clumsy, but not updated to account for the changing touch attack rules. This explains why it doesn't explicitly call out that it carries across multiple rounds.