Over at The Week, a doctor diagnoses some of those cuts, falls and first degree burns:
The injury: Iron to the face
The set-up: Thwarted by the BB gun at the back door, Marv runs around to the basement stairwell — which Kevin has deliberately iced. Once he has stumbled his way down into the dark basement, Marv grabs for what he thinks is the light bulb cord. It's actually a rope attached to a steam iron that is propped up on the laundry chute door. The heavy iron comes plummeting down and smacks Marv in the face.
The doctor's diagnosis: "Let's estimate the distance from the first floor to the basement at 15 feet, and assume the steam iron weighs 4 pounds. And note that the iron strikes Marv squarely in the mid-face. This is a serious impact, with enough force to fracture the bones surrounding the eyes. This is also known as a 'blowout fracture,' and can lead to serious disfigurement and debilitating double vision if not repaired properly."
The injury: Handling a burning-hot doorknob
The set-up: While Marv is getting an iron to the face, Harry tries to enter the home through the front door. The first attempt doesn't go well, as the stocky burglar slips on the icy steps and falls to the ground, landing with a thud on his back. Easing up a second time with the help of the railing, Harry makes it to the front door, reaches for the doorknob — which we see is literally burning red — and grasps the searing handle, the pain of which forces him once again down the icy steps.
The doctor's diagnosis: "If this doorknob is glowing visibly red in the dark, it has been heated to about 751 degrees Fahrenheit, and Harry gives it a nice, strong, one- to two-second grip. By comparison, one second of contact with 155 degree water is enough to cause third degree burns. The temperature of that doorknob is not quite hot enough to cause Harry's hand to burst into flames, but it is not that far off... Assuming Harry doesn't lose the hand completely, he will almost certainly have other serious complications, including a high risk for infection and 'contracture' in which resulting scar tissue seriously limits the flexibility and movement of the hand, rendering it less than 100 percent useful. Kevin has moved from 'defending his house' into sheer malice, in my opinion."
The injury: A blowtorch to the scalp
The set-up: Unable to get through the front door, Harry returns to the back. He kicks his foot through the doggy door to disarm a potential BB gun threat, delicately taps at the doorknob to test its temperature, and, finding it cool, opens the back door — only to unknowingly arm a blowtorch that fires at the top of his head.
The doctor's diagnosis: "Harry has an interesting reaction to having a lit blowtorch aimed directly at his scalp. Rather than remove himself from danger, he keeps the top of his skull directly in the line of fire for about seven seconds. What was likely a simple second-degree skin burn is now a full thickness burn likely to cause necrosis of the calavarium (skull bone)." That means the skin and bone tissue on Harry's skull will be so damaged and rotted that his skull bone is essentially dying and will likely require a transplant.
Read the whole thing here, if you're thirsty for more.