We don't.

[It's not got him a panicky mess or anything, but it's got his paranoia up.]

I'd say somethin' woulda been hard to slip on with us 'cause it was all knees an' elbows in the luggage car and somebody probably woulda felt it. Whatever was invisible could still be felt. I threw some salt for it to go through, and it left these sorta messy salt trails. Tore up a keyboard to scatter as a warnin' system too. They had to go through the keys to get from one side of a hall to another.

So if it's invisible, it's still tactile.

I ain't real confident in nothin' at the moment.