Per 
Photo taken on retrieval of SCP-5XXX instances from ███████ in central London on 07/12/1987.
Special Containment Procedures: Foundation webcrawlers are to search for and purchase all potential instances of SCP-5XXX for sale on auction sites and have them delivered to a secure foundation drop point.
Upon retrieval, the contents are to be electronically counted. Those found to have a definite number of pieces are to be incinerated. Those that return a computer error are to be sent to easy-access storage at Site-██ for testing. As of 25/12/1989 all testing is concluded and further testing is forbidden pending 05 approval. All potential instances are to be directly incinerated.
Description: SCP-5XXX are a batch of children's LEGO sets produced between September and October 1987 for UK toy store ███████, the majority of which were retrieved from the central London branch of ███████ on 02/12/1987.1
Each instance of SCP-5XXX has an uncountable number of pieces. Observation confirms that the number of pieces contained in SCP-5XXX instances are finite. Despite SCP-5XXX's uncountable nature, all Subject-5XXX (regardless of stage), agree upon one fact: The number of pieces in the set is less than it should be, rendering the model uncompletable.
Attempts to count the number of pieces within SCP-5XXX lead to those counting the set (henceforth Subject-5XXX) to go through three stages within the course of the next hour:
- Frustration: Subject-5XXX typically attempt to subitise the number of pieces. However, Subject-5XXX will lose count of the number repeatedly, leading to increased frustration. At this stage, prevention of further anomalous effects is still possible by seperating Subject-5XXX from the set.
- Obsession: Subject-5XXX will begin to become obsessive, attempting other methods of counting the set. So far, observed methods have included (but are not limited to) physical tallying, stacking pieces, and removing pieces as they are counted. None have been successful so far.
- Insanity: Subject-5XXX will begin to display symptoms indicative of a psychotic break declaring there to be a missing piece. What happens next varies, but always ends with Subject-5XXX collapsing dead. Testing has revealed the cause to be sudden total brain death.
Attempts to complete the set normally present no anomalous effects until near completion, at which point the subject will go through all three stages within 10-20 minutes.
Senior Researcher Halden is currently leading further testing into the effects of SCP-5XXX.2
