There are actually 2 of them...
When getting off the ladder at the top (assuming you don't hold down W while going up), don't immediately get out after reaching the top and you start bouncing up and down. Sometimes, if getting off at the right time, you can take damage (I took 1.5 hearts)
Go to the bottom of the ladder (also assuming you don't press any keys), and you will sink to the bottom before getting teleported back up. This doesn't do any damage.
