A perigosto stick was a device which resembled a thin silver probe with a tiny sphere on top. (NA: Love and War) It was used by students at the Time Lord Academy to play games of four-dimensional juggling. (EDA: Seeing I) However, on another occasion, the Doctor claimed that it was a musical instrument. (PDA: Deadly Reunion)
One time, the Doctor and his friend Ruath electrified Cardinal Borusa's perigosto stick. (MA: Goth Opera)
The Doctor was in his early nineties before he could bring himself to admit that he still liked to play with his perigosto stick. The other students teased him mercilessly about that for about fifty years. (EDA: Beltempest)
On one occasion in which the Master believed he had killed the Doctor, he ruefully thought back to youthful hijinks when he and the Doctor had put glue on the Lord President's perigosto stick. (DWN: Doctor Who and the Dæmons)
The Third Doctor once told a humorous story in which the punchline was "never trust a Venusian shanghorn with your perigosto stick." (DW: The Green Death)