1 {scene: St Peter's Square, Rome. Galileo stands on an unlit pyre of wood.}
1 Pope Urban VIII: So, Galileo. Any last words?
1 Galileo: E pur si muove!
2 Pope Urban VIII: Right. Burn him. And get me an amaretto. It's hard work being God's appointed deputy.
3 SFX: JURRRZ! {time machine appears}
4 Pope Urban VIII: What devilry is this?!
4 Isaac Newton: It's science, punk!

E pur si muove is what Galileo is reputed to have muttered under his breath after being forced to recant his belief that the Earth moves around the sun, or face being convicted of heresy. It is Italian, and means "and yet it moves". The legend here is that Galileo was proudly defiant of the Catholic Church, although only in private and not to the point where he would find himself convicted and possibly excommunicated or even executed. Pragmatic defiance, you might say.

Alas, this seems to be merely a legend, as no reliable sources provide credible evidence of what Galileo may or may not have actually said at the time.

A small complication with the phrase is that Galileo spoke Renaissance Italian, in which it would be rendered as E pur si muove. However in modern Italian, the same phrase becomes Eppur si muove. A quick Google showdown shows that the latter is actually more common on the Internet. I'm not sure what this means, apart from the fact that people seem to be more likely to quote Galileo in modern Italian than how he actually would have spoken.

Incidentally, I wrote this strip giving Isaac Newton the line as shown, thinking it sounded awesomely badass and cool. It was only later that I realised that the word "punk", in 16th and 17th century usage, basically meant "prostitute". Consider this passage from Shakespeare's play Measure For Measure:

MARIANA	Pardon, my lord; I will not show my face Until my husband bid me.
DUKE VINCENTIO	What, are you married?
MARIANA	No, my lord.
DUKE VINCENTIO	Are you a maid?
MARIANA	No, my lord.
DUKE VINCENTIO	A widow, then?
MARIANA	Neither, my lord.
DUKE VINCENTIO	Why, you are nothing then: neither maid, widow, nor wife?
LUCIO	My lord, she may be a punk; for many of them are neither maid, widow, nor wife.

What's happening here is... well, no, I don't want to spoil the story if you haven't seen or read it, but Mariana is actually speaking the truth in a way, but Vincentio doesn't understand the circumstances behind it. Lucio is merely a snide character intent on making a rude joke.

Anyway. So not only is Isaac Newton a Clint Eastwood-esque badass interpreting this strip in modern day language, but he's also calling the Pope a prostitute - which is even more badass.