What they're doing is they're eating more than the normal mouse, so they only get fat if we let them  eat as much as they want.
کاری که آنها می‌کنند خوردن بیشتر از معمول است، پس آنها چاق می‌شوند اگر بگذاریم به اندازه ای که می‌خواهند بخورند.