Looking for a scene with an accidental fang drop

Hi! I am making a small analysis video about vampires and I need a scene for illustrative purposes. I recall there being a scene where a character sees blood and immediately reacts with fangs appearing but quickly covers their mouth ashamed of the loss of control.

Something tells me it might’ve been Jessica before she learned the vampire ways but I’m not sure? Can anyone remember the episode and circumstances?

And just in case once again, the being ashamed and covering the mouth is the main thing I’m looking for, not just fangs appearing.