Usually, it's because the sperm gets into the fallopian tube before the egg is released. Once there, the sperm wait for an egg to arrive. After fertilization, it can take 5-10 days for the fertilized egg to begin to attach itself to the lining of the uterus. Pregnancy begins when this happens.
The arrangement of spikes originally had no distinct name; the term Thagomizer was coined in 1982 by cartoonist Gary Larson in his comic The Far Side, and thereafter became gradually adopted as an informal term within scientific circles, research, and education.
The origin of the term ugg is also unclear. Stedman registered the trademark UGH-BOOTS in Australia in 1971, and in 1982 registered the UGH trademark. Frank Mortel claims that he named his company's sheepskin boots ugg boots in 1958 after his wife commented that the first pair he made were ugly..