Snark

The Snark, also known as the Squeak Grenade, is a small, red and bulbous creature, with a large (in relation to body proportion) single green eye and a large pincer-like mandible. Snarks are normally calm creatures that show little signs of intelligence, but if they see any living creature other than another Snark, they immediately begin to attack it.

Snarks seem to colonize in the form of an egg sac and only emerge to attack. They attack aggressively, persistently, and erratically, leaping and biting at their target. After attacking for about twenty seconds, a snark will explode in a spray of acid. Despite their size, they are very dangerous, doing as much as 10 damage with each quick bite (a player can normally take 100 damage). At each bite they release a squeak, which becomes progressively higher in pitch as the time they have left to live shortens. At the end of their 20 seconds, they release a last squeak before exploding.

Snarks as a weapon
Gordon Freeman can obtain an egg sac containing 5 snarks which can be used as weapons. Snarks have an unlimited lifespan while held and still can show an aggressive nature (as two comical idle animations show: one with the Snark struggling to get free and the other with it snapping at Gordon as he teases it with his finger). Once thrown, the Snark's twenty-second life span begins. If there is nothing for the snark to attack, they will return to attack Gordon (which is why the player should be on higher ground than the target when they are thrown).

Each snark is relatively fragile, and a single swing of the crowbar can kill one easily. However, when attacked by snarks, most players will begin to spray wildly with whatever weapon they have at the moment. Given time and experience with snarks, players begin to develop their own strategies of dealing with them, including running backwards and constantly swinging the crowbar to stop any attacks, using the shotgun to kill large groups at a time, or even using explosives such as the MP5/M4 grenade launcher. In multiplayer deathmatch games, snarks provide a useful way of distracting other players (particularly multiple players), facilitating escape or a more leisurely kill. It is not at all uncommon for a player to be seen running through the map chased by a pack of snarks.

These cute little creatures can be used as organic grenades. When thrown with the primary fire button they'll run across the ground in a straight line bouncing off the walls(like the tau cannon). When you release the snark and it goes to a straight line it will bite anything in its path(only once for inanimate objects and some Xen aliens such as Xen grunts and vortigaunts). When you release it, it will seek out human enemies(human enemies include zombies) and then repeatedly jump on them and bite them. There is no secondary attack option. You can carry up to 15 Snarks at a time, and you can release them all at once to cause a tremendous amount of chaos. The pitch of a Snark's chirping will rise over time, and after ten seconds they will self-destruct in an acidic burst. A word of warning - Snarks will not attack most Xen aliens, and if a Snark does not sense a nearby human target they will turn on whoever released them. Snarks will however, attack Race-X aliens. This should be kept in mind when facing them.

Snarks only have 2 health points so any of your weapons can kill them in a single shot; this is easier said than done though as they run and jump around so fast. Furthermore, Snarks always die in small acidic explosions, so it is preferable to kill them when they are still distant. The acidic burst is less damaging than a bite though, so it is worth taking some damage in order to end their attack.

Behind the scenes
A use similar to that of the Snark was to appear in Half-Life 2 for the Headcrab, as the Brickbat.