Shortly after the 11 a.m. opening bell for VIP visitors to Frieze, a collector was seen gasping after stumbling over a pair of black athletic socks lying on the floor of Hauser & Wirths booth. "Is it art?" he muttered, alarmed. Well, yes, it is.

Swiss prankster Christoph Büchel, who back at Art Basel in June made found artworks out of both the keys to his apartment and his wallet, has now made a piece out of a pair of his socks, which look a bit worse for wear. According to the gallery, Büchel doesn't mind if his socks get stepped on or kicked around the booth a bit; by early afternoon, when the socks had separated from multiple kickings, there were two reserves on the unique piece, which is priced at €20,000 ($30,000).

Next door, Lisson Gallery was showing a neon text piece by Jonathan Monk that reads, “Do not pay more than $20,000.” With a different currency symbol (or a stronger dollar) it could function as a guide to purchasing the Büchel. The price structure on the Monk is rather unusual. For its first purchaser, the price is entirely negotiable — this one sold for $10,000 — however if that collector chooses to sell it, the stipulation is that they cannot do so for more than $20,000.

The Monk work is part of a series, with the others rising above the $20,000 on display here. Investors take heed: You’ll have more leeway on the secondary market if you buy the one that reads “Do not pay more than $100,000.”