A vent lets stale air out and fresh air in, so dream books read it as the need to express what has built up. Something crawling through a vent is seen as feelings moving through hidden channels.
Where in your waking life have you met something like this lately?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.