A former night-shift cook at the Denny's restaurant on Illinois Route 3 in Waterloo has been charged with aggravated battery after being accused of contaminating food and watching customers eat it, authorities said Thursday. Police said that Anthony J. Lindhorst, 26, of Waterloo, deliberately contaminated food on at least two occasions by putting his semen into the honey-mustard dressing that the restaurant serves with its chicken strips, said Capt. Suzanne Sweet of the Waterloo police. The incidents occurred in November and April, police said.