Originally Posted by ancientsanskrit
Now I don't know jack about cat physiology, but it would occur to me that in order to have an adverse effect a considerable amount of chocolate would have to be consumed. I really doubt a small amount will do much.
Obviously, don't feed them now that you (and I!) know.
For regular semi sweet/milk chocolate that most of us bake with it does take a bit. Not sure on how much but from being in animal rescue for many years I have yet to hear an experience from someone who's cat ate a little bit and had major problems. And I have heard many of of them.
My youngest (about 7 months) just the other day consumed a homemade loaded chocolate chip cookie (semi sweet kind). This cookie was about 4 inches in diameter and had as many chips as you could possibly fit in a cookie. The only thing that happened was some slightly softer cookie smelling poop about 12 hours later. But most of the time cats will throw up after consuming.
Of course no chocolate should be given but the two things that you really have to be worried about is amount consumed and coco content. The higher the coco (like bakers chocolate) the more toxic it is. The amount for me would have been the whole muffin, since the whole thing is chocolate.
If your concerned then call a vet. But imo unless he is acting out of the ordinary then he will most likely be fine.