What is the definition of vestibule?

Read the passage from animal farm. "that was part of the arrangement! " cried squealer. "jones's shot only grazed him. i could show you this in his own writing, if you were able to read it. the plot was for snowball, at the critical moment, to give the signal for flight and leave the field to the enemy. and he very nearly succeeded—i will even say, comrades, he would have succeeded if it had not been for our heroic leader, comrade napoleon. do you not remember how, just at the moment when jones and his men had got inside the yard, snowball suddenly turned and fled, and many animals followed him? and do you not remember, too, that it was just at that moment, when panic was spreading and all seemed lost, that comrade napoleon sprang forward with a cry of 'death to humanity! ' and sank his teeth in jones's leg? surely you remember that, comrades? " exclaimed squealer, frisking from side to side. now when squealer described the scene so graphically, it seemed to the animals that they did remember it. at any rate, they remembered that at the critical moment of the battle snowball had turned to flee. but boxer was still a little uneasy. how does the characterization of squealer support the author’s purpose? squealer's dramatic accusations draw parallels between him and stalin’s propagandists. squealer's uncertainty shows that he is not a reliable ally of napoleon and is ineffective with messaging. squealer's ability to get the animals to listen to him shows that any animal can rise to be a leader in time. squealer's humble interactions with the animals reflect the importance of equality and cooperation.