His heart is literally trying to burst right out of his chest.
It looks super effective to me. Jessie is known to use excessive force - even on her own friends - to get her point across.
He must have been involved with something that went terribly wrong.
It arguably looks even more scared than Meowth himself.
At least he seems to be regretting it and is living the consequences.
Even if it does make his Cacnea seem a bit jealous.
The do have a history together after all.