Summary
Highlights
Odessa will drop the RPG on the ground if you maintain a certain distance, intending for players to pick it up immediately. The game handles item distribution during cutscenes by either placing them near the player or using console commands to avoid awkward animations, as seen with Alyx and the gravity gun.
You can shoot enemy grenades but not your own. This is because the game considers items thrown by the player as an extension of themselves, and bullets are programmed to pass through them to prevent shooting yourself.
Touching a strider's leg can launch you into the air. This occurs because NPCs use inverse kinematics to ensure their feet always touch the ground. When you jump on a strider's leg, you disrupt this system, causing the strider to mistakenly perceive your head as the ground and quickly move its leg upward.
A glitch allows players to move around after 'dying' if they regain health. This happens due to multiple, inconsistent ways the game detects player death. If your health becomes positive while the game still registers you as 'dying' or 'dead' in some systems but not others, your character can enter a 'swimming' movement state, moving upward and around, similar to underwater controls. This bug also exists in Half-Life 1, though with some differences.
If a crow flies into a barnacle, it gets eaten. However, if you kill the barnacle quickly, the crow flies to freedom. If another object hits the barnacle before the crow, the crow will fly erratically. This is due to the crow's AI, which directs it to specific 'hint nodes.' If the target node is removed (barnacle dies), the crow seeks another, but without further instructions, it can get stuck trying to fly to a non-existent or irrelevant point.
Failing to eliminate all soldiers in an outdoor area can disrupt a cutscene with Alyx and Leon. The soldiers will eventually enter the building, confusing Leon's AI. Instead of turning to call you over, Leon's AI prioritizes seeking cover near enemies, causing him to run to a different spot. The cutscene only resumes when you stand near Leon and look at him within specific limits, not the television screen. Leon remains immune to most player-induced distractions like grenades because a variable tells him to ignore external events, except for finding cover from detected enemies.