Bouncing pokeballs?

[Arphahat]

In combat, I've noticed that occasionally one or more of the pokeballs is bouncing... what does that mean?

 

[DarkEliteKaren]

Those are pokemon that are close to leveling up, I think.

 

[uluuu]

I've noticed that it happens when the type of the Pokemon who's Pokeball is shaking is resistant to or strong against (I get those mixed up a lot) whatever you are fighting. It doesn't seem to take dual types into account though, which is what makes me uncertain about this.

My other theory was that it meant the Pokemon in the shaking ball wants to fight, and letting it do so would make it happy, but I'm not sure if that's like something that would happen in these games. However, Diamond is the first GB Pokemon game I have played since Silver, so I'm not completely sure what is usual or not, anymore.

 

[Arphahat]

Thanks for the responses. I actually was inspired enough to check the manual. It is when they are close to leveling.