<P> Sheldon has sometimes appeared to show empathy, including lending money to Penny without expecting it back quickly (although that may just have been his logical Spock - like response to a problem to be solved; it was, after all, money he was not using and would not miss) and driving her to a hospital when her shoulder was dislocated . Sheldon admits he is overly fond of koalas munching on eucalyptus so much that he has a facial expression that he refers to as his koala face . He dislikes gifts, because the "social contract" in his view creates either a debt or burden on the receiver of the gift which will not stop until one of the two involved in the "gift - relationship" dies leaving the other either in debt or with an undue surplus . Sheldon does not take drugs, not even legal ones such as caffeine, due to a promise to his mother, and is hypersensitive when he accidentally consumes them . It has been shown, however, that alcohol often causes Sheldon to loosen up significantly, although it will also cloud his judgment--on occasion, after drinking alcoholic drinks (both deliberately and accidentally), he has done things that he would never do while sober, such as singing out loud, mooning an audience full of people, confronting Wil Wheaton and affectionately slapping Amy's rear . </P> <P> In response to criticism from his friends that he is mentally ill, Sheldon often retorts, "I'm not crazy; my mother had me tested"--which his mother has confirmed to be true (once while wishing she had gone through with a follow - up examination). </P> <P> Sheldon contrasts strongly with his family, who are neither scientists nor intellectuals . His father George died before the start of The Big Bang Theory, when Sheldon was 14, while his mother Mary is a devout born - again Christian and loving parent . Sheldon has two siblings: a twin sister, Missy, who is a tall, attractive brunette as an adult; and an older brother, George Jr., seen thus far only on Young Sheldon . Both Missy and George Jr. beat up Sheldon during their childhoods, and their mother describes them to be "dumb as soup". Sheldon is very fond of his maternal grandmother, whom he calls "Meemaw" and who calls him "Moon Pie". He called his grandfather, who died when Sheldon was five, Pop Pop . Sheldon was also very close to his grandfather, stating once that his grandfather is the only relative he had who encouraged him to become involved in science . </P> <P> Sheldon has a maternal uncle, Edward, who is called "Stumpy" as the result of a time when he cleaned a wood chipper by hand . Sheldon had another uncle, named Carl Cooper, who was killed by a badger while cleaning a chimney and another uncle that may have done things to children that were legal in Oklahoma per "The Clean Room Infiltration". </P>

How old was sheldon when his father died