The blood's still leaving the head through other pathways, so flowing backwards through a jugular vein may not be dangerous.

血液仍会从其他血管流出头部，因此血液从颈静脉倒流可能并不危险。

The second heart sound, " dub" , is called S2, and the noise comes from the aortic and pulmonic valves snapping shut to prevent blood from flowing backwards after it leaves the ventricles, effectively ending systole.

第二心音“dub”，它被称为S2，声音来自主动脉瓣和肺动脉瓣关闭，以防止血液在离开心室后反流，有效地结束心脏收缩。

A canal that drained the lake into the Gulf of Mexico began flowing backwards as the water level fell, briefly creating the tallest waterfall in Louisiana, while muddy geysers erupted from mine shafts.

随着水位下降， 一条将湖水排入墨西哥湾的运河开始倒流，短暂地形成了路易斯安那州最高的瀑布，同时泥浆间歇泉从矿井中喷发。

The blood's still leaving the head from other pathways so flowing backwards through a jugular vein may not be dangerous, but he says it does show a change in how blood moves through the body while in space.

血液仍然从其他途径流出头部，因此通过颈静脉回流可能并不危险，但他说，这确实显示了血液在太空中流经身体的方式会发生变化。