Do dogs instinctively avoid food that is bad for them? Or not?

[ChickensHaveNoEyebrows]

I'm just wondering, because Jasper is sat in front of me licking his chops while I snarfle a Snickers, and I'm fairly sure that chocolate is poisonous to dogs. Is this something I need to worry about then? Are there likely to be poisonous-but-tempting foods in the house which he will scoff given half a chance?

My dog will dive for a dropped raisin given half the chance and once climbed on to the coffee table to snaffle a half-eaten box of After Eights which he took behind the sofa and devoured several off. Including the paper.

He was fine, fortunately.

My dog will eat anything except mushrooms.
I once tried to trick her by sandwiching a mushroom between two slices of pepperoni. She took the whole lot in her mouth, managed to eat the pepperoni and then delicately spat the mushroom out.

My old girl stole 3/4 of a tier of my wedding cake when mum had left it out, wrapped in foil, after having had the parish priest up for a visit just 2 weeks after I got married.
She also got drunk as a puppy by stealing my sisters glass of wine.

Mum also had to buy a brand new bread bin after she worked out how to open the drop down front and ate a whole new loaf one afternoon.

She would regularly beg for chocolate by smacking you hard on the knee, if you were on the sofa or your shoulder if you were sat on the floor.
She never got any though!

I miss her