Those spikes look similar to the ones at the base of a date palm frond. We have to be careful when handling them because they will stick right through leather gloves. OUCH!
I think blood has some magical magnification property, because it always looks like there's way too much, especially when it's coming from your kid. Glad he's fine.
I remember many many years ago
when I was in first grade, Todd Olsen, a classmate, tripped and hit the bridge of his nose right between the eyes, on the sharp edge of a desk. Must have broken an artery where he hit, because a thin stream of blood spurted straight out like you described. Got all over the classroom until the teacher pinched it off. Todd got taken away in a ambulance. He was fine, but it sure made a big impression on us 7 year olds. I can picture it vividly to this day. Your son will have a great story to tell his kids some day!
Belated happy birthday wishes to you! It may not have been ideal, but it will be memorable!
(Ah, and perhaps the visiting dog was trying to catch that troublesome mouse! Good doggy!?)