Everyone knows that going to the grocery store on an empty stomach is a no-no — you’ll make rash, bad decisions. Research reveals another activity to avoid if you are hungry: arguing with your partner. Indeed, being hungry and angry – hangry – at the same time is never a good combination. New research explains why: lower levels of blood sugar may make people angrier with their significant other and more likely to lash out.

The study was not your garden-variety lab research study—it involved voodoo dolls, pins and loud horns. There were 107 couples in the study and each person was given 51 pins and a voodoo doll that represented his/her spouse. Their blood sugar was measured twice a day for the 21 days the experiment lasted. At the end of each day, they were asked to insert pins into the dolls expressing their anger. The lower the glucose levels, the more pins they inserted. Strikingly, even couples that reported having a good relationship were more likely to insert pins into their dolls if they were hungry.

Being hungry didn’t just cause partners to express anger at a doll. Another phase of the study demonstrated that people who had lower levels of glucose were more willing to blast their spouses with the horns for a longer period of time than those who weren’t hungry.

Bottom line: Avoid arguing on an empty stomach, and broach touchy subjects during or after a meal, not before.

Brad Bushman, the lead author on the study, took the results to heart:

I’ve learned that I should eat a protein bar when I talk to my wife.

As with most things in life, timing is everything.