I had a stray live in the garden for 8 months. He would appear each morning and sit waiting to be fed. When I opened the door he would run away, I would put the food down and he would slowly come back to eat. It took 8 months to socialise him enough that I could pick him up and stroke him...
Apparently, particularly in older cats, there is a vitamin, amino acid, mineral or something like that in grass that they lose the ability to synthesise as they age. Which is why they tend to eat more grass as they get older so I have been told.
But I'm not a vet and have no idea if what I was...