In the tropics, the two oceans behave like neighboring swings. One child pumps by themselves, while the other barely moves until the first gives a push. Similarly, warm water in the Pacific Ocean causes water in the Indian Ocean to change temperature.
El Niño is when water in the Pacific becomes warmer than usual. The Indian Ocean Dipole is the temperature difference between the western and eastern parts of the Indian Ocean. Scientists took 149 years of data and built a model showing who influences whom.
It turned out that El Niño strongly influences the Indian Ocean Dipole, especially in August, when the dipole is just starting to form. The reverse influence, however, is barely noticeable. So you could say that the Pacific Ocean rocks the Indian Ocean, not the other way around.
The names El Niño and La Niña are linked to Christmas: the warm phase often peaks in December, and Peruvian fishermen named it after the Christ child.