The bodies of two dead horses -- killed when a tractor trailer slammed into them on a Delaware highway -- caused another vehicle to overturn early Saturday morning, injuring two people. A 2004 Nissan pick-up truck swerved to avoid the horses, which were lying in the southbound lanes of U.S. Route 13 near Greenwood Road in Greenwood, Sussex County, around 4:30 a.m., entered the center median and overturned, authorities said.