Tom knows Jack can read lies - but if he didn't press the issue, that means it doesn't matter.

"I'd've ripped the arsehole's throat out myself but they--" he sucks in a breath and swallows. "Cross one of their Wards and your flesh peels from your bones. The fire they make goes right through clothes an' burns flesh. They can call up hounds and hawks to kill for 'em if you're out of pistol range.

"I was a feckin' coward, righ' 'en? But for good bloody reason!" Tom is quite willing to punch Jack out if he disagrees.