Kill Moves' mother asks her son for the result of the (principal) square root of 5 to prove he was a savant. Kill Moves provides an incorrect result that Chris acknowledges as correct. The (principal) square root of 5 is (approximately) 2.24.
When Chris appears at the soup kitchen to volunteer, the "Roxy" logo is visible on the side of his ski-flap cap. The Roxy clothing line was not created till 1992 and the show takes place in the '80s.