Continuity mistake: At the end the blood around Francis' mouth keeps changing between shots - blood all over his teeth then not, then back.
Deadpool (2016)
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Directed by: Tim Miller
Starring: Ryan Reynolds, T.J. Miller, Morena Baccarin, Gina Carano
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[Wade is using a bleach pen on his clothes to remove the blood]
Blind Al: Seltzer water and lemon for blood. Or wear red. Dumbass.
Trivia: When Ryan Reynolds goes to the facility to become a superhero, as he's being wheeled through the doors on the gurney, he asks (in regards to when he gets his superhero suit) if it can not be green, and also that it be a real suit and not a CGI one. Both these statements are in reference to the badly-received "Green Lantern" movie which starred Ryan Reynolds in the lead role.
Answer: Yes that would be how she most likely was able to tell.