The Lurm are a diminutive, unpleasant race of magicians and planeswalkers (they originally hail from the distant plane of Jiloth). The Lurm have a rather unfortunate obstacle when learning magic, however; they are utterly incapable of understanding magic. Most sapient races have the facility for the weird mnemonic devices and odd symbols used in typical occult writing, but the Lurm are almost completely devoid of this capability. (The Lurm do innately comprehend exactly one spell, their signature Gloomlight.)
Like most sapient races, the Lurm are resourceful creatures and remain undaunted in the face of adversity. As such, they have since devised a way to capture errant arcane energies and learn spells from them (rest assured that many have attempted to duplicate this ability without success). As such, any spell cast at a Lurm can potentially be captured and learned by the Lurm in question (another reason why this ability is hard to duplicate — try learning how to cast a fireball when it's coming at you at high speed). Once successfully learned, the Lurm can then cast the spell as appropriate.
Lurm can also trade spells and rituals, but expect them to haggle mercilessly. It is typically more trouble than it's worth.
The following Lurm is a somewhat young specimen, only capable of learning lower level spells. It already has a couple at its disposal, but is always interested in learning more. And it is more than happy to initiate magical duels to learn more spells. Other Lurm may already know different spells of the DM's devising, and may be higher level and thus able to catch higher-level spells.
On the subject of Catch Magic: For example, if targeted with Icy Rays from a Level 4 wizard with Intelligence 18, a +1 Magic Staff, and Staff Expertise, the lurm spellseeker can use Icy Rays once in the encounter with a +8 vs. Reflex and deals 1d10 + 5 cold damage. Likewise, if the same wizard attacks with Magic Missile, the lurm spellseeker deals 8 force damage.