Which monsters &/or items can do ‘somatic’ components for the casting of a spell? [closed]


In Dungeons & Dragons, many sentient beings or devices could learn spells &/or rituals. But who is able to perform somatic components normally done by a humanoid of 3′ to 6′ height? Previously StackExchange has suggested this is up to the DM – is such a ruling sufficient here?

Concerns:

  • Oozes: ambulatory… possibly with pseudopods – is this enough detail?
  • Fae: if only 3" tall (6-7 cm) are their hands still large enough?
  • Magic items / animated parts: would an animate embossed cameo within a ring, necklace or coin be enough?
  • Sentient / Awakened creatures: octopi, trees, wolves or squirrels: do paws, branches & tentacles count?
  • Do gesturing images within mirrors (possibly up to full humanoid size) also count?
  • Handicapped: how many fingers/thumbs can one lose and still cast spells?
  • Is giving this ability to illusions, be they permanent, programmed or projected, a logical yet terrible precedent?

Obviously these are all answered just by knowing how much one needs move to trigger somatic components. I cannot find this answer, even in previous versions of D&D.