The minis from Half-Life are mini-headcrabs. They are luckily debeaked, and pose no real threat to agents (of course, if you really agitate one, it might get creative). They will attempt to couple with an agent's head, and while many would view this as a bad thing, having a mini running around trying to latch onto other people's heads is much worse (especially if they attempt it with a Flower). They were first observed by Agents Murtagh and Titus in "Halflife: Fulllife consequences."