How is blood coming from the mouth filmed?

Question

This is not like the other questions such as "how are gunshot and head gashes filmed". How are these scenes filmed where someone is talking and some action is going on such as in zombieland and the people (zombies) start spewing blood. They also just keep on spewing blood for a prolonged period of time on a single scene. How do they do this?

Answer 1

It could be as simple as a blood capsule which the actor bites on cue, or for more, some clever SFX makeup and camera angles covering a thin tube going into the mouth attached to a battery operated pump.