If he will let you, you can try flushing gently with Visine or Murine or similar over-the-counter (human) eye drops. I wouldn't use water or try to pick at the seed at all; there's a chance it has penetrated the cornea partway or fully. If flushing doesn't work, this needs a veterinarian visit. Good luck.

Grass Seed

How To Grow Grass Seed - The Basics

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