Indeed, that animals aren't aware that they are in pain is a remarkable "recent scientific discovery", said Christian apologist William Lane Craig in his debate with me, for example. Craig claimed that all animals other than higher primates lack a pre-frontal cortex, and thus are unaware that they are in pain (see Craig speaking in the video below from about 2 mins 30 secs - P.S. he says e.g. cats have a level of pain awareness, but he maintains science has shown that cats are unaware that they are in pain, which, he says, will be a great comfort to animal lovers like himself).
Actually, that's a load of pseudo-scientific rubbish, as scientists in this new video explain (the video has nothing to do with me btw).
The first responds directly to what William Lane Craig said: "that's not true". (at 6 mins 20 secs)
Another, Professor Bruce Hood, confirms that Craig's key "scientific" claim that animals other than higher primates don't have a pre-frontal cortex is just wrong (from about 8 mins)
Indeed, Joaquin Fuster, the author of a classic textbook on the pre-frontal cortex, says about Craig's statement that it is "wrong on several counts", and explains that all mammals and some birds have a pre-frontal cortex (from about 9 mins 30)
As the commentator points out, "that so many animals possess a pre-frontal cortex is just a google search away."
Several of the scientists also point out that, in any case, even if some animals did have no, or a smaller, pre-frontal cortex, that wouldn't justify the conclusion that they are unaware that they are in pain.
P.S. Hopefully Craig is a straight enough guy to issue an unqualified mea culpa on this one. He's just got the science very wrong.