When you come out of a warp portal, and there is an 
enemy near by, get his attention to draw it closer. 
Keep in mind you have to still be standing in the 
middle of the portal. Let the dinosaur attack you 
until you health reaches zero. Be sure that you don't 
get knocked out of the portal or you will die. If done 
correctly you should be able to walk out of the portal 
invincible. Be careful because the trick will stop 
working when you pick up a health bonus.