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They probably tried to be descreet because they didn't want any sexual connotations on the fact they had an erection. It happens, like you say but it would be a bit awkward during a nonsexual moment.
A mix of three great philosophies, Cynics, Stoics and Epicureans...
You can't trust a bugger any farther that you can throw him,
theres nothing you can do about it,
so lets have a drink!