Many times in the films, R2-D2 is shown lagging well behind the others as they run somewhere, clearly incapable of keeping up, and then when the scene cuts to wherever it is they're going, R2 is right behind them again.

This one is a particularly interesting case.

Transcript

[SFX]: Pow! {Leia shoots a trooper}
Leia: {running up some stairs} We need a fast ship.
Lando: The Falcon then!
Chewbacca: No, a fast functioning ship. The Falcon's hyperdrive still takes an hour to warm up.
Lando: You gave me a lemon?
Chewbacca: No, as I recall you took the lemon.
R2-D2: I'll open this rocked door.
[SFX]: < doop dit boobleep boodit-ting-pow >
Leia: How did you get up those stairs? And—
R2-D2: No time for that now!
[SFX]: < boop nip bip >
{plugs in}
R2-D2: Something's long here!
[SFX]: < bloop fidooby >
C-3PO: What the heaven is right with you, Artoo?
R2-D2: Nothing's long!
[SFX]: < boop bloop >
C-3PO: Your Rs and Ls are the right way around!
Leia: Lando, is that replacement droid offer still open?