Its

  •   The strange animal rubbed its belly.
  •   The angry robot furiously clacked its titanium pincers.
  •   Its time as a doorstop over, the dictionary was shelved.
  •   "Thats it's way of saying it likes you," laughed the xenobiologist.

It's

  •   "It's no wonder the creature attacked," he said.
  •   That's a sure sign it's time to stop applying current to the specimen.
  •   It's a small world after all.
  •   Its funny how that works.