"Wolverine" has Phimosis, and it's "a condition in which the foreskin can't be retracted (pulled back) from around the tip of the penis. A tight foreskin is common in baby boys who aren't circumcised, but it usually stops being a problem by the age of 3. Phimosis can occur naturally or be the result of scarring."

So his skin is maybe too tight, and when he happy, it tears a little since it can't expand as much as it suppose to. The tear hurts!

Circumcise will remove that foreskin and end the tightness and tearing.

Also, circumcise is cleaner. Recommend it!

NHS Page about Phimosis