Mention to students that individual blocks in Scratch and Snap can be tested by double clicking them in the block library so they know this useful, non-intuitive trick for learning what an individual block does.
Misconception: Students incorrectly believe that variables passed into a block in Snap! will get modified; however, a copy of the passed-in variable is what the block receives and modifies.
Misconception: Students think you can use the “item (any) of (list)” block in Snap! and Scratch to check for every item in a list, but this block actually returns a random item.