1. A euphemistic term for being irritable, unpleasant, or just a general bitch. From the study which found that women are better at seeing snakes during PMS, as opposed to other times of the month. Google it.
2. To be pissed off or grouchy.
1. "Man, Jerry's chick totally blew up at me last night over absolutely nothing. That girl must be seeing snakes."
2. "First I had to deal with waiting in line for like an hour, and then my car wouldn't start, and then I burnt dinner and had to eat pickles and Ramen noodles. Jesus, am I ever seeing snakes today!"