What do the numbers that appear when Interceptor "blocks" indicate?

In Final Fantasy 6, the character Shadow can occasionally "block" an attack completely via his weapon (like many characters) but also via his dog, Interceptor. This dog occasionally counter-attacks for large amounts of damage, which is what it is famous for.

However, some of the time when Shadow is blocking, a number appears next to the "blocking-dog-parry" sprite that appears adjacent to Shadow. It appears with the same font color (white) that usually indicates damage to a character, but Shadow's HP is not affected and as far as I know, Interceptor doesn't have HP. This number does not always seem to appear during these dog-blocks.

What does this number mean?

(Bonus points for information specific to Brave New World, which is the version of FF6 I'm currently playing.)