superfetation: fertilization of a second ovum after a pregnancy has begun; results in two fetuses of different ages in the uterus at the same time
fertilization: creation by the physical union of male and female gametes; of sperm and ova in an animal or pollen and ovule in a plant
ketamine: a general anesthetic and tranquilizer (not a barbiturate) that is administered intravenously or intramuscularly; used mainly by veterinarians or for minor surgery with geriatric or pediatric patients; taken in large doses it causes hallucinations similar to those associated with the use of PCP