Hmmmm....

They will only grow to fit the size of the enclosure they are kept in. (Technically something measurable and graph-able, but not sure how you would go about actually experimenting with that. LOL)

They are slimy -- you could measure responses of people touching a snake for the first time? Ask them what they expect to feel...then ask them what they actually felt after they touched it.

They will chase you down -- video different snakes set on the ground and see if they go after a person's feet, or simply wander another direction or try to flee.

Can't think of any other myths off the top of my head. Sounds like something you're going to need to put some creative energy to.