After a bit of testing, I think ! figured out what causes it! :O I found that freezers only fail to trigger when you try to move onto one on the same turn that your sprite would change to the next smaller one! It seems like the function that handles shrinking has priority over the function that handles freezing, which causes the latter to be skipped over, since you can't both shrink and grow in the same turn. So fixing it should be a simple matter of having the two switch placements in the code, yeah?