These two common plants that crop up as garden weeds are both very poisonous. 

The red berries of Lords & Ladies add some nice late-summer colour in shady areas of the garden, but there's a good reason why they don't get eaten by the birds - they're very poisonous.  Thankfully they are so unpleasant tasting that nobody would ever get to eat enough of them to have a dangerous dose.  

The white flowers, one of many different kinds of similar-looking umbellifer is called Fool's Parsley, as it looks superficially like parsley or chervil, but can be distinguished by the small spurs that hang down under the flowers and seed heads.  Like many other umbelliferae, such as hemlock, it's pretty poisonous; though apparently it was also used in the past as a medicine for children's stomach aches - hopefully only in small doses!