Took me a second because I think it the "5 second rule" as "you can still eat it if it's been on the floor for 5 seconds", so I was trying to figure out if the bad guy ate the knife!
I think it IS the 5 second rule, but interpreted as "you can only pick it back up within 5 seconds". Since my mental version specified eating the fallen object, I didn't make the connection immediately. It's just a "me" problem.