"Fi" Combination In Letter

Warning This Section Does Contain Spoilers

The pen pal letter we receive in this episode has a strange typing "error" in all the "fi" combinations. This may not be a typing error or typewriter error. This could potentially point towards the phi Golden Ratio. The golden ratio number starts with 1.618... which is also the same number as John William James' patient number. Maybe this is a special number to him because of this.