Why do I hear a beep (why does my window flash) about 1 second after

I hit the Escape key? This is normal behavior. If your window flashes, then you’ve got the visual bell on. Otherwise, you should hear a beep. Vim needs a timeout to tell the difference between a simple escape and, say, a cursor key sequence. When you press a key in normal mode (and even in insert mode) and that key is the beginning of a mapping, Vim waits a certain amount of time to see if the rest of the mapping sequence follows. If the mapping sequence is completed before a given timeout period, the mapping for that sequence of keys is applied. If you interrupt the mapping, the normal actions associated with the keys are executed. For example, if you have a mapping defined as “:imap vvv Vim is great!!” and you type “vvv” quickly, the “Vim is great!!” will be inserted into your text. But if you type “vv v” then that is what will put into your text. This is also true if you type “vvv” too slowly where “too slowly” is longer than the value for the timeout option. Setting the timeout option to a larger value can help alleviate problems that appear when using function keys over a slow line.