The Friday File: While there is great debate about why yawning occurs, it appears that brain weight and yawn duration are highly correlated and the number of cortical neurons, a measure of brain complexity and yawn duration are spectacularly correlated. For example, a mouse yawn takes about 0.8 seconds, cat yawns last for 2.0 seconds, dogs for 2.4 seconds, camels for 4.8 seconds, and humans a whopping 6.5 seconds.