Roger really didn't know what Eli was asking him to help out with, and he did suspect that Samara probably wouldn't be happy about him helping, if she and Eli were fighting. He had a feeling that it DID have to do with Eli's experiment, since he specifically told him it wasn't.
But whatever. It was his day off, and it felt like forever since he'd seen his best mate. And they were going to go drinking! And Roger was pretty sure he was going to get laid that night. So Roger was happy and feeling good.
He'd apparated to Eli's and let himself in (because he was a best mate, he could totally do that) and Roger found his way to Eli's study. "I figured you would be!" he called back when he heard Eli's voice, and followed it till he was standing in the doorway.
The first thing he saw was a pensieve, and then he really got curious. "So... what are we experimenting with today?"