WHAT DOES MY CAT SEE THAT I DON'T?

Fro the last two hours, my cat, Milton, refuses to leave the bougainvillea at our back fence.
  1. He is adamant that something is in there.
    I can't see or hear a thing.
  2. He's agitated about it.
    Pacing, sticking most of his body in the foliage, staring intently.
  3. Birds have been know to nest in the bougainvillea.
    And there is a mockingbird sitting above on a wire. But mockingbirds will attack if their babies are in jeopardy—we have experience with that!
  4. Milton is meowing like he's being murdered.
    I got a flashlight and searched the bougainvillea again. I'm afraid of what I might find: a dead bird, a dying kitten dropped by the hawk perched on the phone pole this morning, a baby skunk or opossum ... my mind goes into overdrive.
  5. I go back to the patio. Milton runs to me and meows urgently, looking back toward the bougainvillea. Like Lassie, he wants me to come with him.
    I check one more time. Nothing. But I know my cat knows something I don't.
  6. Reluctantly, Milton finally comes inside the house.
    He needs some food and a little nap.
  7. Looking out the window, I see that the mockingbird is back, poking around in the bougainvillea.
    I'm stumped.