not a direct use, but the HEV suit injects the player with morphine if major damage is taken. the only way youre made aware of this is through the HEV suits dialogue.
Throughout the game many of the aliens you will fight are just hostile wild animals from another world. They don't look like real animals, save for the Head-crab who, as the name implies looks like a crab, but the Houndeye creatures do act a lot like dogs.
Some of the aliens are animal-like and it's revealed later that some were experimented on. You aren't given the exact details on the Houndeyes, for example, but you'll enter a room with high security clearance later on where you can zap headcrabs dead on the spot.
I wouldn't say it's dog fighting, but you'll come across a scene where (spoiler) you'll realize that the dog-like Houndeye aliens have secretly been experimented on in Black Mesa. It's unclear exactly what was done to them.
During a couple sequences, notably one in a cage, there is a fish like creature with large teeth that charges the player and they're forced to encounter it underwater
As part of the HEV suit's medical system, Gordon is sometimes injected with morphine. Gordon is presumably fine with it and it has zero effect on gameplay.
There is a scene in which the main character is trapped in a garbage compactor and is tasked with getting out. This will happen to the entire body (treated as a normal death scene) if unsuccessful
A boss towards the end of the game is a giant spider creature with an enormous testicle like organ swinging off of its lower end. The Player will undoubtedly hit it many times during the battle.
No. The only thing I can think of that comes close is a sound you will hear in later chapters of the game that sounds like ghostly/distressed/alien wailing. It's unclear what it's supposed to be.
there is a scientist in early game that is hiding in a dumpster and proclaims he will not leave his "hiding spot", also noting that he did in fact soil himself
There are science rooms with medical equipment like MRIs and an infirmary but not specifically a hospital. Also this game violates the Geneva convention by using the Red Cross
Scientists will begin shaking uncontrollably and start screaming when in danger. Injured Alien Slave enemies will frantically run away from combat and hide from the player
You'll encounter a scientist on top of a generator who refuses to leave until the invasion at Black Mesa is over. Due to actions you must perform in this area, his hiding spot of choice leads to his death. It's hard to determine whether they meant to die that way or not, but it's something to keep in mind.
There are strobe and flashing effects during teleportation sequences or bright flare cutscenes such as a thermal generator or missile being launched. There is also a flashing laptop monitor during "Anomalous Materials".
Not unless you count baby headcrabs. There's also a picture of a real baby in Gordon's locker, but this is just a small detail which can be easily missed.
Not in the original game. But in some expansions like Opposing Force, the heavier guards tend to be played off as comic relief because of their size. You can find one vandalizing a vending machine.
Not in terms of story, no. The black scientist model can be the first one to die depending on how you play the game, but even then, many die offscreen at the trigger point of the plot so it's hard to tell.
The Gonarch, the birthing being mentioned in other comments, is designed after an armoured crab with a giant testicle. this is confirmed to be the intended look by the designers
Blood splatters when people are shot, but with no real physical trauma seen. People explode into low-poly chunks when blown up, with blood splatter. The zombies also have a gory appearance, with an open stomach wound that functions as a "mouth"