According to a study published in Science magazine, brook trout and other varieties of fish exploit turbulent flows swirling around stationary objects in the water to minimize effort and give themselves an energy - saving boost against the current.
अशा स्वेच्छिक कार्यांत, मुलांना सांभाळणे, आजारी प्रौढांची शुश्रृषा करणे आणि घरातील छोटी - मोठी कामे करणे यांचा समावेश होतो.