Con Specimen 1
If you go through the door to the hallway, there is a 50% chance Specimen 1 will pop-up and scare you, BUT they are just cute cardboard cut-outs with a random (NOT SCREAMING) jump scare sound that will give you a heart attack. They are harmless and won't be a problem throughout the game, but if you're being chased by another Specimen, then good luck not stopping the moment when cute cardboard cut-outs pop-up and scare you while another monster is about to kill you.
Con Some of specimen are way too slow and others are a downright nightmare to escape
The fast ones: 2, 3, 4, 6 (they move if you don't pay attention), 7, 8, 9 (in a trap room), 10 (second form), 11, and 13.
The slow ones: 5, 6 (they don't move if you pay attention), 10 (first form), and 12.