nifwlseirff on flickr
I found these hard, nearly opaque balls in Gingy's food bowl, after he finished dinner. The slightly spongy white covering (felt like polystyrene), scratched off to reveal a very hard ball, similar to those in silica gel packets. I fished the emptied sachet out of the bin, cut it open and found another two balls, still in the bottom of the sachet. I have no idea how many more Gingy has eaten!
The suspected contaminated 100g sachet was Snappy Tom, Fresh Catch, Choice sardines with whitemeat chicken.
Safcol have stated that these are actually fish eyes. I've asked if fish eyes are hard enough that a fingernail won't dent them, and apparently fish eyes go very hard when cooked.
For the non-squeamish people, see this post about cooking a tuna eyeball.