Brilliant logical inference. It's completely reasonable to expect someone to know where you've stored items in your own lab they've never been in before.

[He snatched the needle out of her hand, and if she wasn't going to be helpful, then fine, he'd rummage himself: rubber to wrap around his arm, cotton balls and antiseptic, phials for the blood.

Dirk did understand how to take a blood sample for himself. He was just more accustomed to doing it the easy way.]