heres the full scene from Monty python :

Scene 1

[wind]
[clop clop clop]
King Arthur: Whoa there!
[clop clop clop]
Soldier #1: Halt! Who goes there?
Arthur: It is I, Arthur, son of Uther Pendragon, from the castle of Camelot. King of the Britons, defeater of the Saxons, Sovereign of all England!
Soldier #1: Pull the other one!
Arthur: I am, ...and this is my trusty servant Patsy. We have ridden the length and breadth of the land in search of knights who will join me in my court at Camelot. I must speak with your lord and master.
Soldier #1: What? Ridden on a horse?
Arthur: Yes!
Soldier #1: You're using coconuts!
Arthur: What?
Soldier #1: You've got two empty halves of coconut and you're bangin' 'em together.
Arthur: So? We have ridden since the snows of winter covered this land, through the kingdom of Mercia, through--
Soldier #1: Where'd you get the coconuts?
Arthur: We found them.
Soldier #1: Found them? In Mercia? The coconut's tropical!
Arthur: What do you mean?
Soldier #1: Well, this is a temperate zone.
Arthur: The swallow may fly south with the sun or the house martin or the plover may seek warmer climes in winter, yet these are not strangers to our land?
Soldier #1: Are you suggesting coconuts migrate?
Arthur: Not at all. They could be carried.
Soldier #1: What? A swallow carrying a coconut?
Arthur: It could grip it by the husk!
Soldier #1: It's not a question of where he grips it! It's a simple question of weight ratios! A five ounce bird could not carry a one pound coconut.
Arthur: Well, it doesn't matter. Will you go and tell your master that Arthur from the Court of Camelot is here?
Soldier #1: Listen. In order to maintain air-speed velocity, a swallow needs to beat its wings forty-three times every second, right?
Arthur: Please!
Soldier #1: Am I right?
Arthur: I'm not interested!
Soldier #2: It could be carried by an African swallow!
Soldier #1: Oh, yeah, an African swallow maybe, but not a European swallow. That's my point.
Soldier #2: Oh, yeah, I agree with that.
Arthur: Will you ask your master if he wants to join my court at Camelot?!
Soldier #1: But then of course a-- African swallows are non-migratory.
Soldier #2: Oh, yeah...
Soldier #1: So, they couldn't bring a coconut back anyway...
[clop clop clop]
Soldier #2: Wait a minute! Supposing two swallows carried it together?
Soldier #1: No, they'd have to have it on a line.
Soldier #2: Well, simple! They'd just use a strand of creeper!
Soldier #1: What, held under the dorsal guiding feathers?
Soldier #2: Well, why not?

---

Narrative Interlude

Narrator: Sir Launcelot had saved Sir Galahad from almost certain temptation, but they were still no nearer the Grail. Meanwhile, King Arthur and Sir Bedevere, not more than a swallow's flight away, had discovered something. Oh, that's an unladen swallow's flight, obviously. I mean, they were more than two laden swallows' flights away-- four, really, if they had a coconut on a line between them. I mean, if the birds were walking and dragging--
Crowd: Get on with it!
Narrator: Oh, anyway. On to scene twenty-four, which is a smashing scene with some lovely acting, in which Arthur discovers a vital clue, and in which there aren't any swallows, although I think you can hear a starling-- oooh!

---

Scene 23

[gurgle]
Galahad: There it is!
Arthur: The Bridge of Death!
Robin: Oh, great.
Arthur: Look! There's the old man from scene twenty-four!
Bedevere: What is he doing here?
Arthur: He is the keeper of the Bridge of Death. He asks each traveller five questions--
Galahad: Three questions.
Arthur: Three questions. He who answers the five questions--
Galahad: Three questions.
Arthur: Three questions may cross in safety.
Robin: What if you get a question wrong?
Arthur: Then you are cast into the Gorge of Eternal Peril.
Robin: Oh, I won't go.
Galahad: Who's going to answer the questions?
Arthur: Sir Robin!
Robin: Yes?
Arthur: Brave Sir Robin, you go.
Robin: Hey! I've got a great idea. Why doesn't Launcelot go?
Launcelot: Yes. Let me go, my liege. I will take him single-handed. I shall make a feint to the north-east that s--
Arthur: No, no. No. Hang on! Hang on! Hang on! Just answer the five questions--
Galahad: Three questions.
Arthur: Three questions as best you can, and we shall watch... and pray.
Launcelot: I understand, my liege.
Arthur: Good luck, brave Sir Launcelot. God be with you.
Bridgekeeper: Stop! Who would cross the Bridge of Death must answer me these questions three, ere the other side he see.
Launcelot: Ask me the questions, bridgekeeper. I am not afraid.
Bridgekeeper: What... is your name?
Launcelot: My name is 'Sir Launcelot of Camelot'.
Bridgekeeper: What... is your quest?
Launcelot: To seek the Holy Grail.
Bridgekeeper: What... is your favourite colour?
Launcelot: Blue.
Bridgekeeper: Right. Off you go.
Launcelot: Oh, thank you. Thank you very much.
Robin: That's easy!
Bridgekeeper: Stop! Who approacheth the Bridge of Death must answer me these questions three, ere the other side he see.
Robin: Ask me the questions, bridgekeeper. I'm not afraid.
Bridgekeeper: What... is your name?
Robin: 'Sir Robin of Camelot'.
Bridgekeeper: What... is your quest?
Robin: To seek the Holy Grail.
Bridgekeeper: What... is the capital of Assyria?
[pause]
Robin: I don't know that! Auuuuuuuugh!
Bridgekeeper: Stop! What... is your name?
Galahad: 'Sir Galahad of Camelot'.
Bridgekeeper: What... is your quest?
Galahad: I seek the Grail.
Bridgekeeper: What... is your favourite colour?
Galahad: Blue. No, yel-- auuuuuuuugh!
Bridgekeeper: Hee hee heh. Stop! What... is your name?
Arthur: It is 'Arthur', King of the Britons.
Bridgekeeper: What... is your quest?
Arthur: To seek the Holy Grail.
Bridgekeeper: What... is the air-speed velocity of an unladen swallow?
Arthur: What do you mean? An African or European swallow?
Bridgekeeper: Huh? I-- I don't know that! Auuuuuuuugh!
Bedevere: How do know so much about swallows?
Arthur: Well, you have to know these things when you're a king, you know.


an answer provided by wolfram alpha is 25 MPH/40 KMH (but thats for a europian swallo, not african swallow...)

some more links :
http://www.style.org/unladenswallow/
http://www.youtube.com/watch?v=rzcLQRXW6B0&NR=1&feature=fvwp

if someone do ask you this - reconsider if you do wish to work there :)