Scratch

If I define a 'for all sprites' variable called b for the default cat and then define a variable b 'for this sprite only' I can't tell from the variables pane which is which although if I display them on the stage then they say b or sprite1's b. I'll call them global and local from now on.

Now define a local variable called result.

If I now change local b to 1 (so I can tell them apart) and then on the scripts pane put a
set result to b (local b that is) and run it, result becomes 1 (as you'd expect). If I change the b to be global b and run it result changes to 0 (again as you'd expect). Now drag the global b out of the set tile and leave it on the scripts pane, then delete the global b variable.

If I drag the b that's left in the variables pane (local b)  into the set tile and run it I get a result of 1 but I can still drag the b that's on the scripts pane into the set tile and run it: I get a result of 0.

This came up when a student created a bouncing ball physics simulation with a 'bouncability' (= coefficient of restitution) but made it global so every ball bounced the same way. He then made it local so he could have different types of ball, deleted his global bouncability and found that everything had a bouncability of 0.