Pain scales make absolutely no sense and are very difficult to quantify. So, for reference, this is the pain scale I'll be using:

0: No pain whatsoever. Will never show up.

1: What they told you to expect getting a vaccine -- pressure and mild pain, equivalent to getting a needle superficially through your skin while sewing.

2: Pain equivalent to accidentally slicing a finger while chopping veggies.

3: Pain equivalent to a cat scratch.

4: What you actually experience getting a shot -- significant pain, outweighing pressure.

5: Enough pain to involuntarily shout. Very significant.