Enzo is eating dinner in his high chair, and he splashes his hand in some milk that spilled on his tray. he does this several times and seems fascinated by it. then, when his older brother does it, he doesn't seem interested at all. psychologists would say

If Enzo is eating dinner and splashes his hand in some milk that he spilled and is fascinated by it, but when his brother does it he doesn't care, most psychologists would say that he has become habituated to the splashing. That means, he became used to it.