My mum and dad are arguing over something trivial all the time?

OK. We just had dinner, and my dad was calling somebody on the phone during dinner, but he had already finished when my and my mum were still eating. Admittedly, my dad has relatively poor English, and had some trouble communicating with the other guy. I had to prompt my dad on what to say, so I didn't finish dinner. I still had half-a bowl. When he finished on the phone, my mum had just finished dinner, and I still had about a third of a bowl. My mum told me to hurry up, and then my dad, all of a sudden, and completely unprovoked, said "He always finishes quickly when you're not here." Then my mum gets really pissed. This happens all the time, when they argue over something really trivial, like a few spoonfuls of food, and then get pissed completely, with my dad starting the argument most of the time. Why does this happen, and what can I do? Today I was the center of the argument, because my mum was pissed at ME for "letting her down".