As weird as it looks, there actually is about a pixel of safe space at the top of the Piranha Plants mouth. The hit box is a little lower than the actual tip of the spite. It's easy to replicate this jump, you just have to get Mario to jump as high possible.

Poor Ken. He suffered such a terrible plot device to the face so Pete could find himself in a uncomfortable position. I wonder if Ken has much of a future with SC. (Is it just Sterling Cooper again isn't it? I think I lost track of that plot thread.)

I'm wondering if this means we're getting close to finding out why he holds a grudge a against Venture in the first place.