Subtlety aside, Dean knew Sam, and he knew paranoia besides. If Sam wasn't eyeing the holy water, he was definitely thinking about it, and Dean wasn't so far gone he didn't sort of approve. Glancing away from Sam, he looked around until he found the bag and reached down for it, sifting through until he found the holy water and offered it over.
"Next thing we try, we'll have to be real careful. The Mark doesn't like being played with. Normally it just ignores shit thrown at it, but it really didn't like that sword. Freaked it out a bit, had something of a black smoke flare up, so to speak. It's calm now, but it burned like a bitch."