 Later , in the lab at Harvard Walter 's autopsy reveals a synthetic compound in Mark 's blood , though any link to the cuts is not yet known to them . Olivia receives an email from someone who claims to be John Scott , listing an address for her to visit . Upon arriving she finds boxes , one of which contains a group of toads . At the lab , Walter finds that the toads contain a " psychoactive compound " , a hallucinogen that affects the fear center of the brain . They conclude that Mark ’ s brain was so convinced of something happening to his body that actual physical marks appeared . Mark was infected with a large dosage , leading them to attribute his death to murder . 
 Later , in the lab at Harvard Walter <a href='null_genetive' title='1'><mark>'s</mark></a>autopsy <a href='uninflect' title='2'><mark>reveals</mark></a> a synthetic compound in Mark <a href='null_genetive' title='3'><mark>'s</mark></a>blood , though any link to the cuts is not yet known to them . Olivia <a href='uninflect' title='4'><mark>receives</mark></a> an email from someone <a href='null_relcl' title='5'><mark>who</mark></a><a href='uninflect' title='6'><mark>claims</mark></a> to be John Scott , listing an address for her to visit . Upon arriving she <a href='uninflect' title='7'><mark>finds</mark></a> boxes , one of which <a href='uninflect' title='8'><mark>contains</mark></a> a group of toads . At the lab , Walter <a href='uninflect' title='9'><mark>finds</mark></a> that the toads contain a " psychoactive compound " , a hallucinogen <a href='null_relcl' title='10'><mark>that</mark></a><a href='uninflect' title='11'><mark>affects</mark></a> the fear center of the brain . They conclude that Mark ’ s brain was so convinced of something happening to his body <a href='null_relcl' title='12'><mark>that</mark></a>actual physical marks appeared . Mark was infected with a large dosage , leading them to attribute his death to murder . 
Later , in the lab at Harvard Walter  autopsy reveal a synthetic compound in Mark  blood , though any link to the cuts ain't yet known to them . Olivia receive an email from someone claim to be John Scott , listenin an address fa her to visit . Upon arriving she find boxes , one of which contain a group of toads . At the lab , Walter find that da toads contain a " psychoactive compound " , a hallucinogen affect tdafear center of the brain . They conclude dat Mark ’ s brain was soo convinced of something happenin to his body actual physical marks appeared . Mark was infected wid a large dosage , leading them to attribute his death to murder .