Clitoral stimulation in normal copulation happens when the thrusting of the penis moves the clitoral hood. Even though multiple orgasms are very rarely experienced, they are not impossible. Author Mark Levinson considers them to be the ultimate climax women can achieve. For other women, further sexual stimulation can be overwhelming or painful due to clitoral hypersensitivity. The truth is that both are sexual and both are reproductive. She describes typical textbook descriptions of the clitoris as lacking detail and including inaccuracies, saying that the work of Georg Ludwig Kobelt in the early 19th century provides a most comprehensive and accurate description of clitoral anatomy. O’Connell asserts that the bulbs appear to be part of the clitoris and that the distal urethra and vagina are intimately related structures, although they are not erectile in character, forming a tissue cluster with the clitoris. This cluster appears to be the locus of female sexual function and orgasm. It is pleasure separated from reproduction.