Thallium kills. It's an order of magnitude more poisonous than arsenic and just 3 grams of the stuff, less than the weight of a penny, is all that it takes to kill a person. But behind this bullet-proof window called Lucite the little sample within is safe enough that a baby can play with it. Not that that's a good idea, mind you! In addition to being poisonous, thallium is also a finicky metal that is difficult to keep free of surface oxides, becoming leaden gray under oil and degrading to dust in open air. 

Tucked in this plastic container is a small piece of pure thallium kept free of oxides thanks to being encapsulated in a small glass ampule with argon gas.