It is soon swept into the ventral reticulum by ruminal contractions. This behaviour can cause problems such as subacute ruminal acidosis. The main compounds that "S. sucromutans" must obtain from such ruminal fluid are phospholipids. Contractions of the reticulorumen propel and mix the recently ingested feed into the ruminal mat. Their sensitivity to sour-tasting foods helps them to maintain optimal ruminal pH. Ruminal tympany occurs when this gas becomes trapped in the rumen. In addition, it requires ruminal fluid in order to maintain optimal growth. Ruminal tympany may be primary, known as frothy bloat, or secondary, known as free-gas bloat.