What is meant by stupefied ? How has it been illustrated in multiple events till this stage

THe animals are confused and surprised by Napoleon's rule breaking:

Boxer, who seldom says much, actually calls Squealer on his whole "Snowball is a traitor" theory,

"He lay down, tucked his fore hoofs beneath him, shut his eyes, and with a hard effort managed to formulate his thoughts.

'I do not believe that,' he said. 'Snowball fought bravely at the Battle of the Cowshed. I saw him myself. Did we not give him 'Animal Hero, first Class,' immediately afterwards?"

Squealer does not like Boxer's line of questioning. Squealer and Napoleon had re-written history and now Boxer was ruining this. The animals "were stupefied. This was a wickedness far outdoing Snowball's destruction of the windmill..."

Squealer launches into his Snowball conspiracy theory and Boxer finally says what Squealer wants to hear,

"Ah, that is different!' said Boxer. 'If Comrade Napoleon says it, it must be right.' 'That is the true spirit, comrade!' cried Squealer, but it was noticed he cast a very ugly look at Boxer with his little twinkling eyes."

There is, however, the sense that perhaps Boxer is not convinced.