We have a tradition to read certain verses and sections in the Torah in a different tune. The reason for this is that we want to emphasise the content and the mood accompanying these verses.
The endings of all the verses in Shirat Hayam (the song sung by Moses and the children of Israel on the banks of the Red Sea) which is found in the portion of Beshalach (Exodus 15, 1-19), some verses before (Exodus 14, verses 18, 19, 22, 29) and after the ‘Shira’ (Exodus 15:25) are also sung in the same tune. The mood in the ‘Shira’ is one of festivity and joy and so it is expressed by the special tune. The short verses in the Parasha of Mas’ei (Numbers 33:11-35) recounting the Journeys of the Children of Israel in the wilderness are read in the same way as the ‘Shira’.
Another verse read with a different tune is in Parashat Devarim (Deuteronomy 1:12). This portion occurs every year on the Shabbat preceding the fast of the ninth of Av (commemorating the destruction of the Temple in Jerusalem in 70 A.D.). On the eve of the fast, the scroll of Eicha is read with its special tune. The verse in Deuteronomy 1:12 begins with the same word ‘Eicha’ and it is sung in that same tune.