BOX 4.2 How Many? How do 3- to 5-year old children react when they encounter unexpected changes in the number of items? Before the dialog below, children had been playing with five toy mice that were on a plate; the plate and mice were then covered and the experimenter surreptitiously took away two mice before uncovering the plate (Gelman and Gallistel, 1978:172). What follows is one child's attempts to reconcile the differences in the number of mice: Child: Must have disappeared. Experimenter: What? Child: The other mousses?... Experimenter: How many now? Child: One, two, three. Experimenter: How many at the beginning of the game? Child: There was one there, one there, one there, one there, one there. Experimenter: How many? Child: Five--this one is three now but before it was five. Experimenter: What would you need to fix the game? Child: I'm not really sure because my brother is real big and he could tell. Experimenter: What do you think he would need? Child: Well I don't know...Some things have to come back. Experimenter: [Hands the child some objects including four mice]. Child: [Puts all four mice on the plate]. There. Now there's one, two, three, four, five, six, seven! No...I'll take these [points to two] off and we'll see how many. Child: [Removes one and counts]. One, two, three, four, five; no--one, two, three, four. Uh...there were five, right? Experimenter: Right. Child: I'll take out this one here [on the table] and then we'll see how many there is now. Child: [Takes one off and counts]. One, two, three, four, five. Five! Five.