Do you have an obsession? If so, you would probably prefer to think of it as a "collection" lest you potentially be cast as the subject of one of those hoarder shows so popular on TV right now. I'm kidding, of course, although the line between the two anal-retentive categories is probably a bit finer at times than you might care to believe. Today's typo looks as though it likes to collect the letter S and just went a little bit overboard with this one. Actually, obsession and the like are very commonly misspelled words, so this entry is probably more of a spelling error in most cases than a typo made by simply striking the wrong key. It might help to think of it in two parts: ob and session. OB can stand for many things, so take your pick. For example, you might imagine an annual session with your OB/GYN. (However, despite not exactly looking forward to such appointments, I'd say few women are truly obsessed with them.) We compulsively collected nine samples of this typo in OhioLINK, and obsessively obtained 204 more in WorldCat.
(18th-century collection of anatomical models in the Obstetrics Room, Museo di Palazzo Poggi, Bologna, Italy, 2009, from Wikimedia Commons.)