First One
In the Battle of the Cowshed Snowball proves himself a leader and hero by leading the animals, and proves that he knows war strategies extremely well.
Second One
(I believe)
This foreshadows that something may be destroyed in the future hence the "Nothing Short of Explosives". (Explosives destroy things)
(I'm pretty sure the irony is when Napoleon blames it on Snowball even though it was not his doing, but might want to get second word on that)