#51
The bonespew is similar to a web attack, but not quite the same. A web attack is made in the same way as a net attack. This bonespew seems to target all creatures within a spread, forcing them to dodge with Reflex saves.
Should that last part become a separate ability, or even flavor text?
Bonespew (Ex): A THING can spit out a paste made of stomach excretions and ground bone. This breath weapon targets all creatures within a 15-foot diameter, at a range of up to 60 feet. Targets of this pasty spew must make a DC 17 Reflex save or else be immobilized.
Once struck by the Bonespew attack, the target can attempt to break free as a full round action by succeeding at a Strength check against DC 18, or an Escape Artist check against DC 21. The spew-covered victim can also be broken free of the hardened spit; in this case the bonespew has a hardness of 7 and 15 hit points.
THINGs can project bonespew three times before emptying their throat-sack. Each Medium-sized skeleton they devour replenishes one use of the Bonespew attack. Consuming a Medium-sized skeleton takes one round, while digestion of a consumed skeleton takes 5 minutes before it can be used in a Bonespew attack. With access to a fresh supply of skeletons, a THING can use its Bonespew attack indefinitely, pausing only to consume and digest more ammunition.
Rewrote this using the language format from the MM:
Snatch (Ex): A THING can choose to start a grapple when it hits with a tail slam attack, as a free action without provoking an attack of opportunity. If a THING gets a hold on a Medium or Small creature, it can make an automatic claw attack and squeezes each round for automatic tail slam damage. A THING can drop a creature it has snatched as a free action or use a standard action to fling it aside. A flung creature travels 1d6x10 feet, and takes 1d6 points of damage per 10 feet traveled. If a THING flings a snatched opponent while flying, the opponent takes this amount or falling damage, whichever is greater. A THING cannot make a trip attack in any round that it has used its tail as part of a snatch maneuver.
How is this Trip writeup?
Trip (Ex): The dexterity of the THING's tail also allows it to be used to trip opponents, a tactic the THING uses against opponents of Large size or greater. A THING that hits with a tail slam attack and does not use its Snatch attack can attempt to Trip its opponent as a free action without making a touch attack or provoking an attack of opportunity. If the attempt fails, the opponent cannot react to trip the THING.
The +5 seems weird to me, usually it is an even number - but, eh, I digress.

how is this now:
Skills: A THING has a +5 racial bonus on Listen and Move Silently checks.
* A THING receives a +5 racial bonus on Hide checks in areas of low-light or darkness.
Does this section look allright?
THINGs AS MOUNTS
Training a THING as an aerial mount is a daunting task. It requires a successful Handle Animal check (DC 33 for an adult, or 26 for a young specimen). All Ride checks on a THING forced into the open are at +2 DC, due to the affect open spaces have upon the beast's Blindsight and nerves. A THING egg is typically worth 6,000 gp on the open market. A THING can serve as a paladin's mount, though a paladin must be of 9th level and have no current mount before one can be called to serve in such a capacity; providing the creature with skeletons could be a problem for a paladin, though. As mounts, THINGs are usually found only amongst the most martial and disciplined of subterranean races.
CARRYING CAPACITY
A THING can carry up to 459 lbs. as a Light load, a Medium load is up to 918 lbs., and a Heavy load is 1377 lbs. A THING can carry up to its Medium load and still fly.