Learn English – Say “See you tomorrow” in email for an phone interview

The question is broad and actually opinion based. Nevertheless, let me share what I practice.

We address people with Hello in emails quite commonly and this can go for every email you write or respond. However, if you are responding merely with a sentence or two, addressing person directly with their name (as John might have done in this case) is okay.

In another case, if it's the same conversation (more like a chat) having 2, 3 or more mails, I drop Hello and directly address the person with their name.

In this case, as I already said, you may choose any option - Hello John, or John. But if you want to sound a bit formal, go for Hello John,

Jiggle is a certain movement which is caused by an external force which causes a random or pseudo-random movement. Imagine a car driving on a bumpy road, things that might jiggle in the car are

jello on a plate jiggles
the surface of a cup of coffee jiggles
a woman's breasts jiggle ( not initiated by the woman, see below )

When things jiggle they usually remain attached.

Wiggle means not in a straight line. If something has a wiggle in it, it means it curves back and forth (not to be confused with "meandering"). Wiggle can also mean a certain non-straight motion within in a small space, sometimes to create more space.

Wiggling is usually caused by the thing that wiggles.

worms wiggle
paths wiggle, The Wiggle
wiggle wire
a woman's toes wiggle ( initiated by the woman )

When wanting to have less constraints or rules, one can ask for

more wiggle room

Also, The Wiggles are an Australian music group.