As cute as these animals are, the videos/gifs illustrate something interesting about mammalian mental development. Not all demonstrate full self-awareness, as evidenced by mirror experiments. Many dogs bark at their reflection, cats often hiss and arch. Like humans who've suffered brain damage due to stroke or accidents, sometimes they lose awareness of their own limbs (particularly if high on catnip, or if a limb falls asleep from cramping). Hilarity ensues.
Had one cat who was so pissed off at her own tail (which she expressed by flicking, which exacerbated her rage when she noticed it again) that she bit it deeply and promptly screamed. I'm not going to say if I thought that was funny.