But they did't/don't talk when eating.
如果是表达过去的某个动作时,就用didn't;如果是表达他们在吃东西时一般都不说话,表示通常的一个行为,那就用don't
But they don't talk when they're eating.
But they don't talk with full mouth.
But they did not talk while they are eating
望采纳,谢谢
but(however)they don't talk when theyare having dinner;
however they don't talk,when they are eating something.
But they didn't talk when they eating.