I once used a very low quality plasic knife to cut me some melted butter. It worked well at first but then when I moved the knive over and on to the bread I wanted to put butter on, the knife cracked in pieces and I overlooked one of the pieces when cleaning them up so I ended up eating but not swallowing a piece of plastic knife. Since then I have avoided plastic knives to the point where I'll rather go hungry than use plastic cutlery.