What does "a shot off a shovel" mean?

Factual Questions
1

See subject. Early 20th century Ireland.

It’s been suggested that it refers to a turd being shoveled aside. I have no clue.

Anyone?

2

I think “like a shot off a shovel” means “very quickly”, but I have no idea what the derivation is. (Perhaps you knew that, but it isn’t very clear.)

3

I’ve always heard it as “like shit off a shovel”. It’s a not uncommon expression in Australia. I don’t know any backstory but just assumed the imagery was of something slimy flying off a shovel fast and readily.

4

WAG:

A shot of something is a measure or dosage. A shot of medicine for instance. “Give it another shot of cement.” “He is shot full of whiskey.” “I think the deer is still alive, put another shot in it.”

There are shot glasses, the sport of shot-put. We use shot to denote a try “Give the ignition another shot.”

A shot off a shovel makes me think of a shovelful of coal, into a stove or furnace. “Give it another shot of coal.”